Bob Lewis:
What is the best replacement vacuum pump? Is anyone using a wet pump on their O-320? I’m trying to decide where my best position for the M-20 oil separator return line is located.
Editor:
If you haven’t yet bought the wet pump, you should take a serious look at the new piston-type AEON dry pump from Sigma-Tek. I plan to make it my next vacuum pump (near term). Much less expensive than the wet pump, and much less installation hassle. Make sure you get the complete link below. MML may destroy the formatting. See further comments on the M20 following the pump info.
http://www.chiefaircraft.com/cgi-bin/air/hazel.cgi?action=serve&item=/Aircraft/VacuumSystem/DryAirPumps.html#Sigma-TekNew
Sigma-Tek AEON Piston Air Pump
Part No. PHOTO Description CART Price
ST 1U478-003 PHOTO Piston Air Pump, Sigma-Tek ADD $725.00
Direct Replacement: Vacuum or pressure pumps
Bi-Directional Drive: clockwise or counter-clockwise
Clean Sheet Design: Dual action piston pump
Unique Patented Drive Assy: Lifetime permanently sealed bearings
Pumping Chamber is Isolated: No contamination from drive pad
Pump Wear is Insignificant: No particles or dust as in vane pumps
5 year/ 2000 hour Factory Warranty (whichever occurs first)
Replaces All 200 Series: and 1U128 Series rotary vane pumps
Eliminates Installation Errors: Clearly marked vacuum and pressure ports
Unprecedented Long Life: Performance with a warranty to match
Higher Output at Low RPM’s: Gauge stays in the green arc
Hose and System Contaminates: will not adversely affect pump
No Carbon Rotor or Vanes: will not contaminate air system or gyros
FAA-PMA Approved
Regarding the M20 separator, I am a huge fan. If it is installed properly, making certain that the hose routings, drain line angles, separator placement, etc. are all properly done, it works perfectly. It needs to be right at the top of the engine compartment, so that the crankcase vent hose runs as far as possible to the M20, and uphill all the way. The drain-back tube works the best when it is Wye’d into a rocker box drain tube (not Tee’d in), so that the box drain flow creates a small suction in the line from the M20. This requires the welding of a short length of quarter-inch aluminum tube against the side (not bottom) of the main 3/8″ drain-back tube (at about a 45 degree angle in the direction of flow), then a drill bit is run into the new tube to open the passage to the drain line. The tube can then be bent slightly to a suitable attachment angle for obstruction clearance, and the drain hose connected (no clamp needed; just a tie-wrap). The M20 vent tube should exit in the cowling exhaust area, but should be flush with the belly and only very slightly beveled on the aft side. It should not have a large bevel, should not extend into the slipstream, and above all it should not be angled back into the slipstream. The idea is to have vapors exiting straight out with the cooling air, but to have no positive nor negative pressures applied to the exit tube.