When the Laser is shutdown no need to change parameter. The valves in the oscillator close, so continual supply of laser gas mix does not enter the oscillator. But the tubes are at or above atmoshperic pressure with the Laser gas mix.
-You should conduct a automatic internal leak check, note diag and know what your existing leak check is.
-Shutdown.
-with all power off, removed covers of the oscillator.
-remove vacuum pump fill cap, drain oil in a container.
-now be careful removing filter, behind filter cover is a spring, note spring and washer position.
-remove filter, note filter has an oring on the back side of it that fits into the machined slotted surface at the back of the pump housing.
-place new filter with the pleat facing down so vacuum pump oil drains out of it good, and oring is facing back, this needs to seat good or when the laser purges gs you will see a mist coming out of the purge muffler on the side of the resonator.
-now fill about 1.25 cans of the vacuum pump oil, do not over fill, if it is at the line drain some out.
-Now Turbo blower.
-This runs at 200ms or about 60000 rpm's which is why oil needs changed every 2000 hrs and you probably have a 24,000hr blower.
-position hose and drain by the drain valve, while draining, removed the hex bolt with oring on the backside, to allow all oil out, this is where you fill oil back with the little bottle with a clear hose. Close drain valve. Just put the little hose in the fill port and squeeze bottle, note that the sightglass fills slowly, do not over fill, sometimes you wont use all the bottle.
-put bolt with oring back on, tighten but really torqued. If when the laser is starting back up and in seq 18 you see bubbles in the Turbo blower oil sightglass, that bolt/oring is not sealed or oring is bad.
-put covers back on.
-coduct a automatic internal leak check and see if the leak rate is the same. If so you are done.