This pretty well sums it up, from the Sacramento sky ranch site:
"PUMP REPLACEMENT CHECKLIST"
The following pump replacement checklist is also worthy of note:
1. Troubleshoot cause(s) of last pump failure.
Booted aircraft: Check for normal deice timer operation. Timer should inflate boots for approximately six (6) seconds (somewhat variable in pressure-dependent deice systems, but should not exceed 15 seconds for any one cycle). Boots should be pressure bleed-down checked for leaks using Airborne 343 Test Kit.
Inflatable door seals: Check that the system inflates and holds pressure without recycling (no leaks).
Pneumatic autopilots: Check autopilot regulators, servos, and filters per manufacturer's specifications.
Other systems: Check pneumatic camera doors, avionics cooling, etc per aircraft service manual.
2. Replace all system filters.
Failure to change filters may void new pump warranties. Pump inlet filters (pressure systems) and garters (suction) should be replaced once a year or every 100 hours. Central gyro filters should be replaced once a year or every 500 hours (ditto for auxiliary inline filters).
3. Verify correct replacement pump P/N.
Do not merely replace existing pump with identical-part-number item. Consult aircraft Parts Catalogue or pump maker's Application List. Also (if using an Airborne pump), conduct a rotation check. Remove old pump, then manually rotate propeller in normal direction while drive pad gear is observed. (Observe proper safety precautions when turning propeller.) If drive gear rotates clockwise, a 'CW' pump should be specified. If gear turns counterclockwise, order a 'CC' pump.
4. Remove old pump and gasket.
Your old pump (even if damaged) has salvage value; many pump overhauler's will pay $20 or more to have it. Do not reuse old gaskets. New pumps should be mounted on the new gaskets that accompany them.
5. Remove fittings from old pump.
Discard stripped or damaged fittings, fittings with rounded wrench flats, etc. Thoroughly clean and dry serviceable new fittings before using them.
6. Install fitting in new pump.
Here, it is permissible to clamp the new pump in a vice at the base flange only (never at the center housing). Spray clean fittings with silicone lube and allow to dry before screwing them in by hand. "Do not use Teflon tape, pipe dope, or unapproved thread lubes". Tighten fittings down one and a half turns maximum, using a box wrench. Align fittings as appropriate for plumbing connections in aircraft.
7. Check the AND20000 drive pad for oil.
The pad should be dry, with no oil leaking out. Replace pad seal if necessary.
8. Install new pump.
Be sure to lay the gasket in place first, then install the pump. If you drop the pump, discard it. (Likewise, if the pump shows obvious signs of damage, exchange it for another one.) Replace all locking devices. Cinch all four mounting nuts alternately to 50 inch-pounds minimum, 70 inch-pounds maximum.
9. Install hoses.
Inspect hoses inside and out for contamination, condition, etc, and replace questionable hoses. (Replaced brittle or aged hoses to avoid separation of inner layers of hose, which can break loose during handling and be ingested by the pump, leading to premature failure.) In a pressure system that has experienced pump failure, be sure to blow out all lines with compressed air from the panel side, to remove any remaining bits of carbon. Make sure hoses are connected to the proper fittings (do not swap inlet/outlet hoses by mistake).
10. Check pressure/suction regulation.
Run engine to 1,500 rpm and check that suction gauge is reading in the green (or per manual specs).
When replacing a failed pump what should I inspect for
1) A proper functioning pump creates a vacuum in the system lines. When the pump fails internally, the carbon rotor and vanes break into several pieces creating very fine particles of carbon and carbon dust. The vacuum that is present will suck carbon debris back up into the inlet hose possibly contaminating the regulator. In some cases instrument contamination can occur. It is very important to remove the hoses from the aircraft and clean them out thoroughly, making sure to remove all loose debris. It is imperative to clean the entire system after a pump failure. This preventive maintenance procedure will eliminate carbon F.O.D. from entering your new pump.
(2) After you have installed the new replacement pump, We recommend using a commercially available test kit to make sure the aircraft vacuum system is working properly. A faulty regulator , dirty filter(s), or a crimped or partially collapsed hose can cause excessive system vacuum. This increases the load factor on pump and shortens pumps life.
(3) If you have a mid time engine, replace the oil seal in the engine AND 20000 pump mounting pad. This area could be dry now, but, due to age the seal could start leaking in just a few hours allowing oil contamination in your vacuum pump, causing premature failure. Less than $5.00 dollars spent here could save you hundreds of dollars later
