Vacuum Pumps for Alternative Engines.

            There are times when you may want to consider putting a IFR panel in a homebuilt airplane. Many people loudly proclaim they would never fly their plane IFR. While most small homebuilts are not suitable for hard IFR flying, There are many cases where a IFR panel greatly increases the planes utility. Flying above 18,000 ft requires the plane be IFR certified. Flying over Cuba requires an IFR equipped plane. Letting down through a cloud layer requires an IFR certified plane. All these are within the capabilities of a plane like a KR2 if it is suitably equipped. There are many IFR certified steam gauges on the used market which will provide you with an IFR paned. The new electronic flight instruments which are VFR only can be used for “situational awareness.”

            All certified vacuum pumps for aircraft have a splined shaft which is driven from the engine accessory case. This shaft is designed to sheer off if the pump binds to protect the engine. This shaft cannot stand any side loading such as that presented by a pulley and belt drive.

Rapco Website     Expected life of Rapco Vacuum pumps    Measuring Rapco Vacuum Pump wear    How to Maximize Vacuum Pump Life

I have found two types of belt drives and a third type which is direct drive.

Revmaster System

The system used by Revmaster uses a modified Airborne pump Part no. 211CC-11. (See photo).

            This pump has been modified by the addition of a double roll ball bearing and a drive shaft designed to accept a pulley driven from the engine. The pump modification appears to be in the front section of the pump case. If the pump failed, the front section of the pump could be swapped with a standard pump to get you going again. The pump is probably rebuildable with a standard rebuild kit. The bracket to mount this pump is a simple slide or pivot bracket with a bolt hole pattern to accept the pump.

Dan Diehl System

             This system is no longer sold by Dan Diehl. The bracket that the pump mounts to has a provision to press a double roll bearing into it. A special shaft is inserted into the bearing, then a standard mount dry vacuum pump is bolted to the bracket. The pump holds the shaft in place.

             The shaft is part of a gear set that has an internal spline. The shaft comes our of a Continental engine and is ground to size and cut to length.  The bearing is a double roll ball bearing  # SNR 5204.ZZG15 or a TRW# 5204CFF(0002)LOB.  With this system, you can bolt up a standard pump as a replacement.  Either a 215CC or a 216CW pump will work with this system.  (This is the system I am installing on N51GL.  I am using a 216CW facing aft)

Direct Drive System

  A third option is to direct drive the pump from the firewall end of the crankshaft. The pumps can turn a maximum of 4000 rpm, but any speed above 2400 will cause dramatically increased wear.  There is no side load, but make sure there is no oil leaks that could get into the pump. The biggest problem is the required space from firewall to crank. A internal spline adapter must be made for the end of the crank. This type of drive is used on the Jabiru engines.