A gas ballast is a regulated in-bleed of a dry gas (usually Air/Nitrogen) into the compression portion of the pumping cycle of the vacuum pump. The gas acts as a stripping agent that will mix with the contaminating vapors present in the pump and expel them out the discharge of the pump. Gas ballasts are usually installed as a standard component on all oil lubricated rotary vacuum pumps to aid in the removal of condensable vapors from the vacuum pump oil, prevents contamination of the oil and can be used to clean contaminated oi. Please refer to the manufacture’s manual on the proper usage of gas ballast valves.
SCFM stands for Standard Cubic Feet per Minute. ACFM stands for Actual Cubic Feet per Minute. SCFM is the air volume measured at “standard conditions” which refers to atmospheric pressure (14.7 PSIA) at sea level elevation and a temperature of 68 Deg F. ACFM represents the air volume pumped at the pressure, elevation and temperature your system is operating at.
When dealing with vacuum leaks, you must first determine if the leak is an actual leak (“Real”) or if it is an outgassing situation in the chamber (“Virtual”). Outgassing comes from any liquid (water, solvents, process material, etc.) that is vaporizing inside the vacuum chamber either off the chamber walls or out of a product placed into the vacuum chamber for processing.
One method to determine the type of leak is to do a “rate of rise test”. To perform this test simply pump down on the chamber until the lowest recordable vacuum level is obtained. With the systems vacuum measurement gauge, measure the rise in pressure over time in the chamber. If the pressure eventually rises to atmospheric pressure then the leak is most likely external in nature. If the pressure rises and stops at some pressure below atmospheric in a 24-hour period then the leak is most likely from the process.
For external leaks the use of a Helium leak detector maybe used depending on what size of leak you are looking for. Another method of finding external leaks is by spraying a small amount of acetone around the suspect leak areas and when the acetone enters the vacuum system there will be a spike in the pressure you will see on your vacuum gauge. Use caution with this method as acetone is very flammable.
Outgassing situations can also be verified by measuring the vacuum in the system with a McLeod gauge. Since a McLeod gauge can only measure permanent gases (air, nitrogen) and not vapors then a low pressure reading with a McLeod gauge and a higher pressure reading with a total pressure gauge will indicate an outgassing situation.
There are many issues that can prevent a new pump from obtaining its’ ultimate pressure. Assuming the pump is new and just recently installed, the most common cause is a small air leak somewhere in the system upstream of the pump. Quite simply, if the air leakage coming into your vacuum system is greater than your pumps’ ability to remove it, then you will have trouble maintaining your desired pressures. If the vacuum pump does not have enough pumping capacity to handle this additional air in-leakage, it will not be able to maintain the vacuum level you desire. Outgassing in the system is also another common reason you will not see the desired vacuum level and this is process independent and will need to be evaluated on an individual basis.
Commonly mis-diagnosed as smoke this is mechanical pump oil vapor. It is normal for the pump to emit vapor when pumping on a chamber from atmosphere or high pressures. Since all the mass that is removed from the chamber by the pump moves through the oil in the oil reservoir, some of that oil is vaporized when a lot of mass flow is moving through it. When the pressure in the chamber is reduced below a few hundred Torr, the oil vapor or "mist" should reduce dramatically. It is normally recommended to install an oil mist eliminator on the exhaust of your mechanical pump to reduce it even further.
This is very process dependent. There are virtually endless situations that will affect oil life in a vacuum pump. The manufacture will provide baseline numbers to reference as a general guide. One method to use is the oil needs to be changed when the pressure in the manifold the pump is pumping on cannot achieve the level you have previously recorded when the pump was known to be in good working condition. The safest way to determine when the oil needs to be changed is with regular oil sampling. This will determine the state of the oil and its performance in your pump.
The easiest way is to take multiple pictures of the pump and send it to Northwest Industrial Repair and let us try and identify it for you.
It is process dependent. Please refer to the manufactures manual for the pump or contact Northwest Industrial Repair to guide you to the appropriate selection for optimal performance/life of your vacuum pump. It is critical to use the proper oil, again for performance/life. “Standard” oils are not intended for use under a vacuum and will not perform correctly in your system.
Before starting the blower fill the oil reservoir sumps through the oil fill plug or breathers until oil appears in the center of the oil sight glasses. Verify oil level is at the proper level in both gear end and drive end sight glasses. For M-D Pneumatics® CP series oil/grease lube blowers (A6), oil fill is located in gear end. Refer to the blower operator manual for approximate oil capacity per blower model. Operation of the blower without proper lubrication will cause the blower to fail and void the warranty.
One of the top three root causes of blower failure is a result of improper lubrication and quality of oil used in positive displacement blowers and boosters. The lubricant is selected based on bearing speed, gear speed and operating temperature. If the lubricant is too light, it increases wear by not separating the sliding surfaces and it will not remove the heat adequately. If the lubricant is too thick, the drag in the bearings is increased, causing them to run hotter. Thicker lubricant will not flow as readily into the gears and it will reduce the available backlash.
If you are interested in learning more about the benefits of proper oil and lubrication for blowers and vacuum boosters, check out this article by M-D Pneumatics®: