Welch Vacuum 1376N Chemstar - Manual (Page 31)

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Part 5 Recommendations For Pumping Particulate-Containing Gas Streams
A. Particulate Trap With A Filter Element
A particulate trap provides positive protection for vacuum pumps when dusty or loose particulates are pumped on. These
particulates are formed in some chemical reactions involving corrosive gases in applications such as coating, powder
materials processing, etching, etc. A particulate trap with fi lter element is available through Welch
(See Section 2 C.)
The particulate trap will reduce the effective pumping speed of a CHEMSTAR pump-particularly as the element collects
particulates. You can see 50% loss of the pumping speed for pressures below 1 Torr. This is why some prefer to use an
oil fi ltration system to remove the particulates once they get into the vacuum pump without hurting the pumping speed.
B. Oil Filtration System
Many applications in chemistry, material science or metallurgy generate abrasive particulates. These particulates are
ingested by the vacuum pump and will lead to a deterioration over a period of time in the operating characteristics of
the pump as most evident in the ultimate pressure. A particulate trap or an oil fi ltration system is used to remove these
particulates to minimize this effect.
If you cannot use in your application a particulate trap because it reduces the pumping speed too much or the corrosive
gas attacks the polyester element, Welch recommends the use of an oil fi ltration system. In addition, some elements will
also remove acidic compounds from the oil. See Section 2 C. for details.
Part 6 Extending Service Life of CHEMSTAR through Proper Maintenance
A. Developing A Maintenance Schedule
After Studying many examples of pump failure, Welch has found the most common reason is poor condition of the oil.
This is why a regular maintenance schedule for the oil is critical to obtain the longest service life out of your CHEMSTAR
pump.
Welch recommends that you examine the condition of the oil on a daily basis in the early days of a new process or
experiment. You want to look for discoloration of the oil and whether the oil level is rising. The discoloration can indicate
deterioration of the oil and a rising oil level can indicate condensation of vapors is occurring in the pump.
Once you know how long it takes for the oil to breakdown in your application or become contaminated, review the Welch
accessories mentioned which are listed in Section 2 C to see which will work best in your application or choose this time
as your oil change interval.
B. Forced Oil Flushing
When you drain oil through the drain valve, you are not removing the oil and contaminants that are inside the pumping
mechanism. You are removing oil only from the oil case. Welch recommends a forced oil fl ush of CHEMSTAR pumps be
performed at the regular maintenance oil change. The procedure for the forced oil fl ush is given below:
1. Check the oil level
a. If the oil level is well above the fi ll mark, this may indicate either the pump has been overfi lled with oil or has
ingested a liquid or a large amount of vapor (water or organic solvents). Please go to step 2.
b. If the oil level is even with the fi ll mark and you do NOT suspect corrosive gases or particulates (henceforth
called contaminants) ingested have damaged the mechanism, run the pump for 15 minutes to allow the pump oil to warm
up before going to step 2.
2. Turn off motor for the vacuum pump. Drain the oil into a clear plastic container (may need pliers to open drain valve).
Look for contaminants settling to the bottom of container. If you see contaminants, you will need to repeat step 3 through
5 several times until the oil comes out clear. The oil you drained from the pump came from the oil case only. There may
be contaminants in the pumping mechanism. To be sure all contaminants have been removed, the pump mechanism
needs to be fl ushed.
3. Make sure the belt guard is installed before proceeding further. Attach a short hose to the drain valve which runs into a
clear plastic container.