Many shops use vacuum chucks to hold workpieces, especially in the aircraft and aerospace industries. The heart of the vacuum system is the vacuum pump. Without a reliable source of vacuum, parts can’t be held down. So, how can you make sure your vacuum pump is healthy and stays reliable?
What Type of System Do You Have?
The first question to answer is, “What type of vacuum system do you have?” In some shops, each machine has its own pump. In others, there is a central vacuum system that is distributed around the shop. In both cases, it’s important to know what should be checked and maintained to ensure steady service.
For smaller shops, most machines will have their own individual vacuum pump. These are typically electric pumps, and may be dry or oil lubricated. There are also vacuum generators that use compressed air and a venturi pump to create vacuum. These are typically used for very small chucks.
Check Your Vacuum Pump Capacity
First, vacuum pump capacity should match the requirements of the vacuum chuck you are using. For example, each vacuum pump will have a vacuum capacity and flow rate specification. Full vacuum is defined in a variety of units, including negative PSI and atmospheres. One atmosphere of vacuum is equal to about -14.7 PSI of vacuum. That is all we can get on planet Earth! Have a look at your pump’s vacuum curve to see what vacuum is possible at given flow rates.
Some vacuum pumps can provide nearly full vacuum, but cannot tolerate losses due to leaks. As the flow increases, due to seals on your chuck leaking, the vacuum available from the pump drops. This can cause great problems if it happens while you are cutting your part. Stronger vacuum pump designs are capable of providing full vacuum and reasonable leakage flow rates. You must maintain the seals on your chuck to insure your vacuum pump fully supports your vacuum clamping system.
It is also a good idea to mount a vacuum gage to your chuck so you can see exactly how much vacuum is getting there.
Keep an Eye on Your Coolant
The next big problem you face is coolant management. Coolant, or cutting fluid, is already a big enough problem to maintain (health & safety) in the shop. The problem becomes worse when using a vacuum chuck. It is nearly impossible to prevent coolant from being sucked into your vacuum chuck during cutting and on down the line to the pump. Even the best o-ring seals will leak, and there will always be some coolant ingested between parts. What can this ingested liquid do to your vacuum pump?
If your vacuum pump is a dry type (no oil), coolant can quickly contaminate the seals and mechanical parts of the pump itself. If you add some chips to this, you only compound the problem. If your pump is oil lubricated, the coolant will not only interfere with the pump impeller movement, it will also quickly contaminate the lubricating oil.
So, how can you keep coolant out of your expensive vacuum pump?
The most obvious answer is with some kind of liquid separator, like a filter regulator, right? Yes, that is true, but a typical compressed air filter/regulator/separator cannot filter out the volume of liquid required in a vacuum system. They are designed for ounces. We must be able to handle gallons. So, we have to take it to the next step and rely on some new technology.
Consider a Liquid Separator
There are a variety of liquid separators available designed for vacuum systems. The most basic are installed in between the vacuum chuck and the pump. There is a rigid tank (to support the vacuum forces) and filtering material that separate the coolant from the air flow back to the pump. At some point, when the storage tank is full, the machine operator is required to stop the pump and drain the tank back into the machine coolant tank. For larger, central vacuum systems, it is possible to have this type of system built with large storage tanks and automatic draining.
Another solution is to combine a vacuum pump and coolant separator into one unit. The coolant is separated and stored in a tank just below the vacuum pump, which adds the benefit of a vacuum reservoir. A float switch is used to warn the machine operator when the coolant level is nearly full and must be drained.
You may now be wondering, is it possible to design a vacuum pump that is not contaminated by liquids? Yes, there is. A liquid ring vacuum pump uses water, or water based coolant, as an integral part of pump design. The coolant is drawn into the pump and used as a seal. With this type of vacuum pump, only a drain hose back to the machine is required. It is never necessary to manually drain the pump. When the liquid level in the pump reaches an overflow, excess coolant drains back into the machine coolant tank. No operator intervention required.
As with all equipment, follow the suggested maintenance schedules for the pumps, filters and oil. By maintaining your equipment, or, replacing some vacuum pumps with newer technology (liquid separators, liquid ring vacuum pumps) you can enjoy the benefits of a strong and reliable vacuum system in your shop.
|Stand Alone Liquid Separator||
Combined Vacuum Pump & Coolant Separator
|Liquid Ring Pump|