When it comes to selecting the correct vacuum pump for your application there are a number of issues that need to be considered. There is a vast array of vacuum pumps available: Rotary Vane, Diaphragm, Screw and Turbo pumps, just to name a few. The two main specs required for selecting the correct pump are the vacuum level and the flow rate. Once these have been established the range of pumps available for your application will be less confusing.
The next thing you need to look at is the application itself. Is it a clean room application? Is it a large industrial job where there is plenty of water vapour?
These elements need to be discussed and considered carefully. The next subject is the material of the pump. Some applications are subject to a high amount of corrosive or acidic vapours, so Teflon or stainless steel will need to be a major component of the pump. Some pumps however cannot offer a high grade of protection so a special type of oil is required. This is the case with rotary vane pumps.
Power supply is another important aspect. This can be single phase, three phase, DC supply; sometimes even frequency converters are necessary.
It is important that you also consider the type of protection required. The pump could be in a hazardous area, which could possibly cause an explosion if the motor is not of the correct protection class.
As you can see there are a number of variations and performance elements that need to be taken into account when selecting a vacuum pump for your next job. If you are unsure about what is available or need assistance then please contact us for expert advice.
Ultimate vacuum will not be instantaneous. It is relative to pump capacity and system size. If it appears the rotary pump is not achieving high vacuum, check as follows:
Oil level correct when pumping.
All fitting hoses are tight and valves shut.
If no improvement is achieved, check with a known good McLeod gauge or electronic gauge as follows:
Remove pump from system.
Connect gauge to suction fitting positively sealed.
Run pump. A McLeod gauge should indicate a vacuum of between 50 and 1 micron. An electronic gauge will show approximately 250 to 20 micron after five minutes, depending on the type of pump.
It is extremely important to operate your vacuum pump using the correct viscosity oil, as those that are either too thin or too thick will cause damage and operational issues.
Oil MUST be changed when contaminated.
Oil contamination is usually indicated by poor vacuum reading, or a grey or milky appearance. Should liquids be accidentally allowed into the pump CHANGE OIL IMMEDIATELY. Your High Vacuum Pump is a precision unit and oil is less expensive than pump service and repairs.
We take pride in every Vacuum Pump we supply and ensure you of our long-term interest in our product’s reliability. To ensure your continued satisfaction, Coolvac highly recommends the following oils for each model vacuum pump:
Product recommended oil for standard application
(See Part #s below)
DD/CD 40 No. 15
DD/CD 75 No. 16
DD/CD 150 No. 16
DD/CD 300 No. 16
Your XTR Pro or EVO Series recovery unit can be used to PRE-cool (or SUB-cool) the recovery cylinder if the head pressure is too high to complete the recovery process. This can occur when working with certain refrigerants with a high vapour pressure in high ambient temperatures.
If the recovery process stalls out because of high head pressure, stop the recovery unit, shut off the hose valves and reconfigure the setup as shown below. This can also be done before starting the recovery process but it may have marginal long term effect. NOTE: This will only work if there is at least 5 kg of liquid in the recovery cylinder to develop the necessary pressure differential required.
Power on the recovery unit and rotate the discharge valve (V3) to achieve a pressure differential of at least 700 kpa between the LP gauge and the HP gauge. Keep the HP below 2500 kpa on the HP gauge to ensure that the HP cut-off switch will not actuate.
After several minutes of running, the cylinder will be cold. Power off the recovery unit and reconfigure the setup for normal recovery. Repeat as needed.
Your air conditioner is designed to automatically remove unwanted heat from your home. Understanding and caring for your unit ensures a longer life, maximum efficiency and saves repair or replacement costs.
Basic split system units are comprised of an evaporator coil, a condensing unit, and refrigerant lines. These parts work with the fan and control system in the air handler to cool your home.
The cooling cycle starts when the thermostat senses that the home’s air temperature is above the thermostat set point. Contacts in the thermostat are closed and control voltage (24 vac) is supplied to the air handler control board. This causes the blower on the air handler to start.
The air handler control board then supplies control voltage to the outdoor part of the system, called the condensing unit. This control voltage causes a device called a contractor to close its contacts. This supplies power to a fan and to a pump that is referred to as a compressor.
This pump raises the pressure and temperature of the refrigerant gas in the system. This high temperature and high pressure refrigerant passes through the outdoor coil. This coil (called the condenser coil) works the same way as the radiator on a car but it uses refrigerant instead of water. In the condenser, this high pressure refrigerant is cooled and condenses from a gas to a liquid. It is usually cooled to a temperature about 20 degrees below the saturation temperature and is called sub cooling.
This high pressure/low temperature liquid refrigerant is pumped to the indoor section of the system. Then the refrigerant passes through a metering device which regulates the flow to the evaporator coil. In smaller and older systems this device consisted of small copper tubes called capillary tubes which lowered the flow and pressure. Others use specialised flow restrictor devices. Modern high efficiency systems use a device called a thermostatic expansion valve. This device senses the refrigerant temperature at the outlet of the evaporator and automatically adjusts a valve to regulate refrigerant flow.
These devices cause the refrigerant pressure to go down. Air is circulated over and through the evaporator coil by the fan on the furnace/air handler. Heat from the home’s air is transferred to the refrigerant. This heat raises the temperature of the refrigerant above the saturation point and it changes back into a gas. The flow of refrigerant is regulated so that extra heat is added above the saturation temperature. This is called superheat and is added to ensure that the refrigerant stays in the form of a gas as it goes through the compressor. This refrigerant gas is then pumped back to the condenser where the process repeats itself over and over.
When the thermostat senses that the home’s temperature is below the set point, the contacts are opened and control voltage is no longer supplied to the furnace or the air conditioner.
The size of an air conditioner is expressed as tons of cooling capacity. A ton is equal to the ability of the system to remove 12000 btu of heat per hour. Btu stands for British Thermal Unit and is a standard measure of heat.
The relative measurement of a unit’s energy use to perform this cooling is its SEER rating. SEER stands for Seasonal Energy Efficiency Ratio and is a ratio of the cooling output divided by the power input. In general terms, the higher a unit’s SEER number, the less electricity it requires to produce the rated amount of cooling.
Higher efficiency units typically have some special features. They usually have two stages (speeds) of operation. In some cases this is accomplished by having two compressors in the unit. One is run on low speed and both are energised for high speed. In other cases, this is achieved by having one compressor with two motors inside. One motor is energised for low speed and the other is energised for high speed operation. On some high efficiency units the condenser fan motor can operate in low or high speed too.
The highest efficiency air conditioner uses an advanced compressor called an inverter drive. This compressor has a motor that runs on direct current (DC) instead of the normal alternating current (AC). This DC power can be easily varied to provide almost an endless number of speeds. This allows the unit to precisely match the cooling requirements of the home and can save a lot of energy.
If your air conditioning problem is that the unit is not working at all:
Check the thermostat very carefully to ensure it is turned on (a common mistake!)
If your thermostat is a wall mounted digital type and it is totally blank, check that the batteries are not dead.
Ensure the thermostat is turned to ‘cool’.
If the problem isn’t the thermostat or remote, check the breaker.
Check that the unit has not simply been turned off.
Before you turn it on, make sure no one is working on the circuit that breaker supplies.
When you’ve determined it is safe, turn the breaker on.
If the air conditioner runs, cools, and keeps running, you’ve solved your air conditioning problem.
If the breaker is in the middle, tripped position, turn it all the way off.
After checking no one is working on any equipment in the circuit, turn the breaker on and see if the a/c will run.
If it runs, cools, and stays on, make sure that the indoor and outdoor fans are running, and make sure the evaporator (indoor) and condenser (outdoor) coils are not dirty or blocked.
Listen to the compressor for several minutes.
If you hear the compressor starting and stopping but the condenser fan seems to be running normally, turn off the unit and have someone check the compressor. It may need new start components.
If your breaker trips again after running several hours or even a couple of days, you may have an intermittent air conditioning problem that you should have a professional technician check.
The possible problems include:
a worn breaker
a loose, dirty, or corroded wire connection
pitted contactor contacts
condenser fan overheating and stopping
wires grounding or shorting out
compressor winding failing
fan motor winding failing
If your breaker trips instantly as soon as you try to turn it on, stop and have a professional technician check your unit. Possible causes of this issue are direct short or ground in the wiring, compressor windings or fan windings, or a direct short or ground in relay, contactor, or transformer windings.
One reason not to keep resetting a breaker that trips instantly is that the shorted or grounded wiring could be sparking when you reset the breaker, and it could be a fire hazard.
Here are some examples of additional air conditioning problems that could be caused by repeated
The problem may be that your air conditioning unit just doesn’t seem to be cooling as well as it should.
Check the indoor air handling unit.
Make sure the filter is clean.
Make sure the coil is clean.
Make sure the blower is clean and running.
Make sure nothing is blocking the air flow in and out of the indoor coil.
Check the condensing unit.
Make sure the coil is clean and that nothing is blocking air flow through it.
Make sure the fan is running.
If the problem persists, see a professional technician.
If your air conditioning problem is a water leak:
Clear the drain of the indoor air handler, using a wet/dry vacuum cleaner and vacuuming the end of the drain outside the building.
While you have the vacuum cleaner out, open the indoor air handler and vacuum the rubbish out of the pan you’ll find underneath the coil.
If you can, take a look at the corner of the pan the drain line is attached to.
If there is debris there, clean it out.
If your air conditioning unit is making a strange noise:
If it’s a humming/buzzing noise, open your unit and look for a loose panel screw, fan bracket screw, pipe clamp, piece of insulation, or even a noisy relay or contactor.
If it’s a rattling noise, again, look for something loose in or on the unit.
If you hear your compressor making a grinding or hammering noise, it may be failing mechanically.
If a fan is squeaking, the bearings are probably drying out and may require a professional lubrication by a technician lubricate.
Using your air conditioning charging station in the winter months can present its own problems. The refrigeration gas (R134a) does not flow too well if the external temperature drops. Some machines have their own on-board heaters but others rely on recovering some refrigerant from the vehicle or from a supply cylinder. One of the benefits of recovering and recycling refrigerant is the heat generated through the compressor. The charging station works exactly the same way as a vehicle: if you draw gas from a low pressure area and compress it, the low pressure side gets cold and the high pressure side gets hot. This hot high pressure liquid that comes from the recovery side gives us a benefit when charging into the car as the liquid races into the system quicker.
One of the drawbacks with charging liquid refrigerant into an evacuated system is that as soon as the liquid is released it wants to expand into a gas and equalise the pressure between the car and the charging station. If this takes place before the full charge has been delivered then the station effectively undercharges the car and the charge is not complete. A simple trick to rectify this is to close the red HP valve on the station or the HP coupler and start the car. The compressor on the vehicle will then pull the rest of the refrigerant into the vehicle and finish the charge. The gas charge is usually weighed in from a scale platform on a modern machine and the scale doesn’t care how the refrigerant is decanted.
If you find that there is a regular problem with charging, check that the vacuum pump is in good condition. The oil level and oil condition is critical. The vacuum pump oil lubricates the pump and provides the seal for the pump blades. If the oil level is too low, the seal breaks down and the high vacuum required cannot be reached. The quality of the oil is also important.
A poor vacuum can cause many problems because it does not dehydrate the system properly. Any moisture in the car’s system can be devastating, as the combination of R134a and moisture creates hydrochloric acid. This quickly saturates the filter dryer making it useless and then starts to destroy the whole system from the inside out.
With the winter months being cold and damp, moisture is very difficult to keep out of an open system, especially if the vehicle has been damaged and stored for a while. Because the system is effectively charged with refrigerant (R134a), as soon as it escapes and evaporates it leaves the inside of the system very dry. Moisture is automatically attracted to the dry areas and considerable amounts of water can form inside the pipes and condenser. This is unavoidable and only an extensive evacuation can rectify it. In this case a new filter dryer must be fitted and the system evacuated immediately. If we break into the system and have to leave it for any length of time then taping the open hose ends up with tape can be a great help. This obviously stops moisture and dust from entering the system and causing unnecessary contamination. A good vacuum gauge can be critical in determining when sufficient vacuum has been achieved to sublimate (remove) moisture.
A very cold car can be difficult to recover the gas from. This can be due to the pressure being very low in the system and warming the car up is a great help. Also, if the recovery cylinder has picked up air (remember air cannot be condensed) the pressure increases and the compressor will struggle. As a tip, it is always worth keeping the new supply cylinder near the station so that they are at the same temperature.
In most recovery applications we are all in a hurry to recover the most amount of refrigerant in the quickest time available. This can be made easier by using the ‘Push-Pull’ method. Otherwise you must ensure that your recovery unit does have the refrigerant throttle to it via the manifold to prevent liquid slugging, which will cause damage to the compressor.
In all applications you should wherever possible have your cylinder under vacuum and as cool as possible. This will also help speed up the recovery process.
What is the Push-Pull method?
In simple terms, you draw vapour off the top of your recovery cylinder, run it through your recovery unit and then back into the system you are recovering from. Next, run a hose from the liquid dipper tube on your receiver to the liquid in your bottle.
This method is only useful when more than 7kg of liquid is known to be in the system and it can be easily isolated.
The actual requirements on Recovery Machines are minimal but important!
Keep the unit clean by wiping it down with a damp cloth to remove dirt, oils, etc. prior to storage for the day. Standard household detergent or isopropyl alcohol may be used if the unit is particularly dirty; in all cases, exercise care to prevent liquids from entering the unit. Gasoline and other solvents are to be avoided as they can damage the plastic enclosure and are hazardous.
Clean inlet particle filter regularly. Discard internal filter screen if it is heavily contaminated and replace with a new screen.
Ensure that the Inlet and Discharge ports are protected and kept clean by replacing the plastic caps after every use. For best results, keep a filter permanently connected to the suction line port in a similar fashion to the filter in a liquid line.
Change hoses periodically as they develop leaks and a build-up of contaminants over time. Change hoses at least once per season. Especially change the little rubber gaskets inserted into the hose end fittings. If a Schrader Valve is inserted into the end hose fitting and the rubber gasket is worn, the end to end connection will almost certainly leak !!
When storing the recovery machine for the season, or for long periods of time, purge the unit with an inert gas such as Nitrogen.
When performance falls off it is likely that the compressor seals require replacing. This is normal with use and may occur after a year or two or more often, depending upon the conditions that are prevalent during the recovery operations.
Air conditioning is the process by which air is cooled and dehumidified. The air conditioning in your car, your home and your office all work the same way. Even your refrigerator is, in effect, an air conditioner.
Air conditioning systems operate on the principles of evaporation and condensation. The principles of evaporation and condensation are utilised in your car’s A/C system by a series of components that are connected by tubing and hoses. There are six basic components:
Thermostatic expansion valve
Refrigerant is the life blood of the A/C system, a liquid capable of vaporising at a low temperature. Due to the harmful chlorofluorocarbon (CFC) in the formerly used R-12 refrigerant, all vehicles built after 1996 use R-134A, a more environmentally friendly refrigerant.
Here’s how an air conditioning system and its components work:
The compressor is the power unit of the A/C system. It is powered by a drive belt connected to the engine’s crankshaft. When the A/C system is turned on, the compressor pumps out refrigerant vapour under high pressure and high heat to the condenser.
The condenser is a device used to change the high-pressure refrigerant vapour to a liquid. It is mounted ahead of the engine’s radiator, and it looks very similar to a radiator with its parallel tubing and tiny cooling fins. If you look through the grille of a car and see what you think is a radiator, it is most likely the condenser. As the car moves, air flowing through the condenser removes heat from the refrigerant, changing it to a liquid state.
Refrigerant moves to the receiver-drier. This is the storage tank for the liquid refrigerant. It also removes moisture from the refrigerant. Moisture in the system can freeze and then act similarly to cholesterol in the human blood stream, causing blockage.
As the compressor continues to pressurise the system, liquid refrigerant under high pressure is circulated from the receiver-drier to the thermostatic expansion valve. The valve removes pressure from the liquid refrigerant so that it can expand and become refrigerant vapour in the evaporator.
The evaporator is very similar to the condenser. It consists of tubes and fins and is usually mounted inside the passenger compartment. As the cold low-pressure refrigerant is released into the evaporator, it vaporises and absorbs heat from the air in the passenger compartment. As the heat is absorbed, cool air will be available for the occupants of the vehicle. A blower fan inside the passenger compartment helps to distribute the cooler air.
The heat-laden, low-pressure refrigerant vapour is then drawn into the compressor to start another refrigeration cycle.
Almost every vehicle’s A/C system works this way, however certain vehicles may vary by the exact type of components they have.
It is rare to have many problems with modern auto air conditioning. Most problems that do arise stem from one of two things: no cool air or insufficient cool air. If you own an older car and its A/C system doesn’t seem to be working properly, here are some general troubleshooting tips:
No cool air – possible problems:
Loose or broken drive belt
Inoperative compressor or slipping compressor clutch
Defective expansion valve
Clogged expansion valve, receiver-drier or liquid refrigerant line
Leaking component: any of the parts listed above or one of the A/C lines, hoses or seals
Insufficient cool air – possible problems
Low refrigerant charge
Loose drive belt
Slipping compressor clutch
Slow leak in system
Partially clogged filter or expansion valve
Most A/C repairs are best left to an expert technician. Recharging the refrigerant in particular requires special equipment. Contact Coolvac’s team of experts to discuss your issues.
When recovering gas from a vehicle, ensure it is done at a moderate pace. Most automotive A/C systems take on average 100-150ml of oil. This oil is circulated with the gas around the system and at any one time. If too much oil is removed from a system the compressor will fail prematurely. Most automotive recovery machines have an integrated oil separator. This separator is only so efficient at extracting the oil from recovered gas. If gas is recovered too fast, users run the risk of the oil being pumped into the reclaim bottle and thereby are unaware of how much oil the system is short of.
As a general rule, recover from the low side of the vehicle A/C system first. Limit the speed of recovery by throttling the valve on the recovery unit. When the majority of the gas has been recovered, the high side may be used to recover. This ensures no liquid refrigerant carries excessive amounts of oil back into the recovery unit.
Heat Pumps are a heating and cooling device suited for either residential or commercial applications. As well as being versatile, heat pumps are also extremely energy efficient – it can save up to 370% of your total electricity – that means for every $1 you spend on electricity to run your heat pump, you could receive up to $3.70 worth of heat.
Rather than converting electrical energy to heat, a heat pump uses electricity to power two fans and a compressor. The act of compressing the refrigeration gas provides the heating or cooling used by the system. It works on the principle of transferring heat from one place to another against its natural flow.
Another common term for a heat pump is a Reverse Cycle Air Conditioner.
The simplest versions are designed for a single room and the most complex for a whole house or commercial space. It takes 20 to 40 minutes to bring a room up to the desired temperature, which should then remain within one or two degrees. There is no energy used as there would be with an electric bar heater or column heater. Electricity runs a fan and compressor.
Heat Pumps (like refrigerators) have a system of pipes containing gas (refrigerant) that is continuously expanding in one part of the system while compressing in another. When the gas is being compressed, it gets hot. A heat pump’s exterior unit compresses the gas and then pumps it to the interior unit, where the gas runs over a series of finned coils, giving off the heat.
The gas is then returned to the outside unit, where it expands and runs through another set of finned coils, which become cold. The cold gas is then recompressed – and so the cycle continues. For summer cooling, the refrigerant flow is reversed, so the interior unit becomes cool, while the exterior is hot.
If pump won’t run, is turning on and off repeatedly, or not producing enough heat, check for the following:
Check the unit is switched on (this is more common than you would think!)
If there is no power, check for blown fuses or tripped circuit breakers. If any breakers are tripped, reset them once. If they trip again do not reset them. Deadly high voltage conditions exist inside the air handler cabinet and inside the access panel of the condenser and only a qualified technician should open them.
If the air handler runs constantly but cannot satisfy the thermostat setting, it is possible the backup heat is running but the condenser is not.
If pump is overloaded, wait 30 minutes then press reset button on outside cabinet. Repeat if necessary.
Check the coil is not blocked with dirt, debris or ice – remove if found.
If the reversing valve is stuck, put on emergency heat and call a professional technician.
The filter may need cleaning or replacing.
If the thermostat is programmable, ensure the batteries are fresh
The greater the ballast valve is open, the more oil aerosols (oil vapour) will be discharged from the pump and therefore the quicker the oil level inside will reduce. The lesser the valve is open, the greater likelihood water will remain trapped in the oil. A happy medium needs to be found !
IT IS VITALLY IMPORTANT THAT THE PUMP HAS REACHED ITS NORMAL OPERATIONAL TEMPERATURE (50-70oC) BEFORE ANY CONDENSABLE VAPOURS ARE PUMPED. FAILURE TO DO THIS MAY CONTAMINATE THE OIL AND DAMAGE THE PUMP. SUCH DAMAGE WILL VOID THE WARRANTY.
Normal operating condition is at which a slight “popping” noise occurs. With the pump running against a closed suction port and at its normal operating temperature, a definite change in sound occurs when air is being admitted through the ballast valve. Open valve a little before closing down to required control position. With Javac vacuum pumps, If valve is removed ensure spring and ball are replaced in the correct order – spring first. Note that most other vacuum pumps with ballast valves fitted are of the “O” Ring type and if opened too far, may vibrate open even further. An alternative gas ballast valve construction method in higher priced pumps is of the “Two or Three” Position rotary knob type. In every manufactured method, the basic theory is to admit various quantities of air into the appropriate pump generator cycle.
Allowing the pump to run for a few hours with the ballast valve open and the inlet port closed off will purge oil slightly contaminated condensed vapours i.e. water. The gas ballast, if used during start up of the pump will aid in bringing the pump up to its operational temperature sooner.
Care must be taken when operating the ballast valve that the body of the pump is not touched, as the normal heat generated by the pump in normal operation is in the order of 50-70oC.
Note: The greater the ballast valve is open, the more oil aerosols (oil vapour) will be discharged from the pump and therefore the quicker the oil level inside will reduce. The lesser the valve is open, the greater likelihood water will remain trapped in the oil. A happy medium needs to be found !
What is the purpose of the Air Ballast (Gas Ballast)?
The air ballast valve is situated at the top of the vacuum pump next to the suction fitting. It is opened by turning anticlockwise. The valve must only be shut down finger tight otherwise the precision valve seat may get damaged.
The function of the gas ballast valve is to enable condensable vapours to be discharged through the pump with minimum oil contamination, depending on the nature and quantity of the vapour(s) involved. As vapour will condense back into its liquid form upon compression at (or greater than) its Saturation Vapour Pressure (SVP) this can present a problem with high vacuum pumps which have a suction and a compression cycle. It is necessary during the compression cycle of the pump to compress the system gas from the suction port at or greater than atmospheric pressure in order to lift the exhaust valve allowing them to be discharged. In a vacuum system containing a quantity of water for example, the air is quickly removed by the vacuum pump and the partial pressure of the water in the system will increase. When the partial pressure of the water vapour of the system gas reaches it SVP during the compression cycle of the pump, it will condense back into a liquid and mix with the oil.
At this stage the vacuum pump CANNOT achieve a vacuum better than the SVP of the water. This is because the water evaporates from the oil on the suction cycle and then re-condenses back into the oil during the compression cycle. The water in the oil therefore becomes a source of vapour that the pump must contend with! If however we reduce the partial pressure of the water vapour during the pump’s compression cycle with a measured and controlled amount of non-condensable gas the water vapour WILL NOT reach its SVP during compression and will therefore be discharged from the pump. The gas ballast valve in most pumps ‘meter in’ a controlled amount of atmospheric gas into the compression cycle of the pump, thus ‘diluting’ the amount of vapour that is being compressed.
All high vacuum pumps have a maximum amount of water vapour tolerance i.e. the quantity of water that the pump can successfully pump without contamination. (Please contact if you are unsure with the amount of water or any other vapour that your pump will handle.)
Note: the above is in accordance with the normal operation of a standard Javac vacuum pump. Operational differences are minimal in comparison to other manufacturers pumps.
In the following information, we have used resources not just from our own library but also information gained over the years from Cuddon, Telstar, and Leybold where this information has been supplied by these companies over time in the general conduct of our business. Therefore we wish to acknowledge these companies in publishing any of the following information.
The not very secret understanding of the principles of freeze drying are directly related to water vapour pressure and the related state of water in three forms. Ice, Liquid, and Vapour (Steam). All of us interact daily with water in the forms described whether it be making ice cubes to put in our drinks, water from the tap, or boiling water for hot drinks and watching the steam (water) vapour dissipate as the vapour is discharged from the kettle and disappears into the air, eventually becoming part of the normal humidity around us. The vapour is still there, you just cannot see it !
As water vapour is either pressurized like the hot water in your car radiator or reduced in pressure using a vacuum pump, the water vapour temperature rises and falls according to the related pressure. In your car, the boiling point of water is raised to allow higher temperatures to exist in the water cooling system. A good example of pressure reducing and at the same time the related water vapour temperature reducing can be seen on the weather maps we view most days in the media. The low pressure areas are generally a slightly lower pressure than the usual atmospheric pressure experienced at sea level.
Cyclones, Hurricanes, and similar storms exhibit even lower pressures during these occasions. However, the pressure needed to freeze water when higher temperatures exist needs special equipment with the ability to create a vacuum, trap any water vapour on a colder surface as ice, and keep the item being freeze dried warmer than the trapped ice ! This process can only be conducted using a vacuum chamber and vacuum pump engineered for the purpose, a refrigeration surface to trap the ice, and a means of putting heat into the product being dried. This is a little more complicated than it seems and hence the item of machinery has been developed we call a freeze dryer.
In our opinion, leak detection is the single most important subject within the refrigeration industry when relating to climate change and the future of you and your families. The containment of refrigerant has two very important related issues. The more we contain, re-use, or recycle refrigerant, the less ozone depleting substances damage the atmosphere which leads to the second reason, less refrigerant imports are required for new installations or for maintenance purposes. It’s a “Win Win” situation and comes right down to the importance of this subject. We make no apologies for repeating this dialogue in our blog.
The equipment to be tested is pressurized with a gas, search gas, or a search gas mixture. Between the two methods there exist many variations depending on the particular application.
Pressure Drop Method.
The test object is filled with a gas (for example air or nitrogen) until the testing pressure is reached. Precision gauges are used to detect a possible pressure drop during the testing period. This method is simple to implement, it is suitable for the determination of gross leaks and can be improved upon by using differential pressure gauges.
The test object is filled with the search gas or the search gas/air/nitrogen mixture to which the leak detector is sensitive. The leak detector is equipped with a sniffer probe, whereby there is a low pressure at the probe tip. If the sniffer tip passes suspicious points on the test object the search gas coming out of the leak is sucked in and transferred to the detection system of the leak detector. After conversion into electrical signals these are displayed optically and acoustically by the leak detector.
Hand held leak detectors using the detection of pressure escaping through the leak source by listening for gas leaking. These leak detectors are very efficient but are limited by the need for absolute quiet during the detection procedure.
Evacuate the system using a vacuum pump. A vacuum pump cannot achieve a vacuum better than the Saturated Vapour Pressure of any moisture (water) or other contaminants that may be in the system or vacuum pump. This is because water or other contaminants that may have been drawn into the pump evaporates from the oil on the suction cycle and then re-condenses back into the oil during the compression cycle of the pump.
Ultimate vacuum will not be instantaneous. It is relative to pump capacity and system size. If it appears the rotary pump is not achieving high vacuum, check the following. Is the oil level correct when pumping. Are all fittings, hoses and mechanical joints tight and valves shut. If no improvement is achieved, check the vacuum pump with a known good McLeod gauge or electronic gauge by removing the pump from system, connect the vacuum gauge to a suction fitting positively sealed. Run the vacuum pump. A McLeod gauge should indicate a vacuum of between 50 and 1 micron. An electronic gauge will show approximately 250 to 20 micron after five minutes, depending on the type of pump.
System must be evacuated to less than 1.0 Millibar absolute. After the system has been evacuated the vacuum pump should be isolated from the system. As a guide, with constant ambient conditions, the vacuum should not rise more than 0.13 Millibar in one hour. A greater rate of rise may indicate a leak or the presence of moisture. Absolute vacuums must be measured using accurate measuring equipment selected for the specific application.
With this method it is only possible to determine the total leak rate. After the test object is evacuated with a vacuum pump or a vacuum pump system, a valve is used to isolate the test object from the vacuum pump. The pressure will then rise as a function of time. Pressure rise can exist due to outgassing from the surfaces of the test object. This pressure rise tends to tail off in the direction of a saturation level. If in such a case the time allowed for monitoring the pressure rise is too short, a leak will be indicated which in reality does not exist. If one waits long enough for the pressure to rise, the outgassing process can then be disregarded, so that the leak rate can be determined from the known volume of the test object and the measured pressure rise over a fixed rise time. In practice, where outgassing and leak rate are added together, the detectable leak rate depends on the volume of the test object, the obtained ultimate pressure and the outgassing from the test object. In connection with a very large test object, this method is time consuming if extremely low leak rates are to be determined in the fine and rough vacuum range. In practice, we have found a recorder to be useful in these circumstances.
A helium leak detector permits the localization of leaks and the quantitative determination of the leak
rate, i.e. the gas flow through the leak. Such a leak detector is therefore a helium flow meter. In practice the leak detector performs this task by firstly evacuating the part which is to be tested, so that gas from the outside may enter through an existing leak due to the pressure difference present. If only helium is brought in front of the leak (for example by using a spray gun) this helium flows through the leak and is pumped out by the leak detector. The helium partial pressure present in the leak detector is measured by a sector mass spectrometer and is displayed as a leak rate. This is usually given in terms of volume flow of the helium.
The two most important features of a leak detector are its measurement range (detection limits) and its
response time. The measurement range is limited by the lowest and the highest detectable leak rate.
The following rule of thumb for quantitative characterization of test vacuum equipment may be applied:
Total leak rate < 10-6 mbar·l·s-1: Equipment is very tight Total leak rate 10-5 mbar·l·s-1: Equipment is sufficiently tight Total leak rate > 10-4 mbar·l·s-1: Equipment is leaky
Table; Comparison of bubble test method (immersion or pressurise technique) with helium leak detector
Gas Loss Time taken to form Equivalent Detection time using
per year a gas bubble leak rate helium leak detector
(g/a) (s) (cm3[STP]/s) (s)
280 13.3 1.8 . 10-3 a few seconds
84 40 5.4 . 10-4 a few seconds
28 145 1.8 . 10-4 a few seconds
14 290 9.0 . 10-5 a few seconds
2.8 24 min 1.8 . 10-5 a few seconds
0.28 * 6 h 1.8 . 10-6 a few seconds