Chemglass AF-0350 Welch Vacuum Pump - Manual (Page 10)

3.3 Oil Changes and Oil Level
3.3a 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 DUOSEAL 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 conden-
sation of vapors is occurring in the pump. When changes occur, the oil needs to be change. If no changes in
the oil level or color are observed, extended pump service life is obtained if the oil is changed every three to
four months.
3.3b 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 flush of
DUOSEAL pumps be performed at the regular maintenance oil change. The procedure for the forced oil
flush is given below.
1. Check the oil level.
If the oil level is well above the fill mark, (This may indicate either the pump has been overfilled with oil or has
ingested a liquid or a large amount of vapor water or organic solvents.) Please go to step 2.
If the oil level is even with the fill mark and you do NOT suspect corrosive gases or particulates (hence
forth 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 contaminations 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 flushed.
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.
4. Flushing the pump is carried out by adding a cup of DUOSEAL vacuum pump oil through the intake port
(IN) while the pump is turned on for 15 to 20 seconds. While adding the pump oil, the palm of your hand is
placed lightly over the exhaust port (OUT). Look for water coming out of the drain. Turn off the pump.
5. Repeat step 4 until clean oil comes out of the drain hose.
6. Fill the pump with the amount of DUOSEAL vacuum pump oil your pump needs.
7. Plug the intake (IN) port with a rubber stopper. Turn the pump on and run the pump for 10 minutes. Close
the gas ballast.
8. Check the vacuum reading of the pump by connecting a thermocouple gauge tube to the pump’s intake. If
the pump is running nearly as good as when it was new, the total pressure reading you will read on wither
of these two gauges will be at least 10 micron.
A simple way to connect the gauge tube to the pump is to run the threaded tip of tube through a hole in a
rubber stopper. Use pump oil as a lubricant for inserting the tube. The stopper chosen should be bigger than
the outer diameter of the intake flange.
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