As a result of a PM asking about whether or not a Perry Pump would stop fuel siphoning, I decided to try it and see. I have two Perry's in service, but on one there is just straight pipes which precludes muffler pressure, and on the other the distance from the tank to the engine is too far. Neither has the tank centerline well above the spray bar. This will be no surprise to folks who have tried it, but may help others decide. On both the VP-20 and the VP-30, the fuel started running through the pump as soon as a head started to develop. My conclusion is a Perry is good for a low tank but not so good when used when the tank is high.

That makes sense, Tim. [sm=thumbup.gif]

Perry pumps use reed valves that only prevent backward flow. They will pump from a low tank but do not overcome G forces very well.

Thanks Tim, I posted this in another thread and was told I was wrong.

Is it important where the pump body of the VP30 is mounted ? Could it be "too high" or "too low" ??

Why would anybody use a pump when you had such good head pressure (e.g. high tank)?

Oh well, some have more time to fiddle around than to fly, I guess.

Cheers,

Chip

Chip, if a person was tempted to use a Perry Pump in a high tank situation, thinking it would regulate the flow and prevent flooding, this test shows it would not.

Flyer95, this is from the manual: "The pump is best mounted horizontally and on the same level (as close as possible) with the carburetor."

The VP 30 does regulate pressure, but at a pressure much higher than that from a tank mounted too high. So the fuel pours right through. Perry Pumps were designed for 70's type pattern planes with bored out carbs to supply more fuel with weak vacume from the carbs. They do work well with tanks mounted far from the engine as well. But use a Cline regulator if you want it to stop dripping fuel.

To quarantee fuel flow when inverted and glimbing but Chip I quess this was [:-]

Good observation Tim. Perhaps needle valves are closed more to cause any problems IRL. I have taildraggers and when on ground the tank is low and no siphoning happens.

When P30 fails does it fail suddenly or does it decrade gradually?

esamart, I think "fail" is the wrong word. I've used both the 20 and 30 without problems. As soon as the fuel level was above the pump, a trickle started.

Sorry for confusion. I understand that is normal even with good and operative P-30. I have got any trouble in my use. I just tried to gain general experience about P-30 which I am planning to use soon after many years. I have one used and one unused which have bright aluminium case so they are old.

Cline is the best device to make the tank location not matter to the engine.

Well, I see your fuel bottle and the two pumps. I don't see your test setup. Did you stand that fuel bottle on end and connect it to the Micro Oscillating pump, then drop a fuel line from the pump's outlet a foot or two below that? If you did it that way, you were stacking the deck in favor making the pump siphon.

If you laid the tank on its side and located the pump at a height approximately equal to the tanks location, you'd have it set up like it would be in an airplane. Then, of course, you'd have to connect the pump's outlet to an engine carb, with the throttle closed. Only then would your test approximated a real model installation. Why not rig it up on an engine test stand?

CR

Charlie,

If he positioned everything like you say, the fuel wouldn't siphon enough to be a problem anyway?

It doesn't matter whether you have the 20 or 30, they will both pass fuel with a positive head of fuel on the inlet.

Charley, I said it was a simple test. I think all I remember doing is filling my fuel bottle, connecting it to the inlet of the pump, blowing on the vent line of the bottle to prime the pump and then raising and lowering the bottle to vary the head on the pump.

Maybe it's the way I set it up. I had an inverted ST .60 in a Sig Kommander. The carb fuel inlet was below the CL of the tank. I mounted the pump opposite to the usual way; the plate was mounted on what would be to the top screws on the engine backplate if the engine was upright, but upside down in relation to the head. This put the pump inlet near the tank CL, and the outlet line only dropped ~1/2" to the carb inlet nipple. There wasn't much of a pressure head that way and the pump didn't dribble. I also always took care to keep the throttle all the way closed between flights in order to reduce any tendency to siphon. I also used muffler pressure and a third line for filling. I was told that the pump wouldn't work, being so near the crank but I guess those Sig aluminum mounts were flexible enough to let the pump work. Before I put the pump in, the engine would load up in the midrange. The pump cured that tendency. I flew it that way for several years, no problems. That was a nice model. It had the first sheeted foam wing I ever built.

I wouldn't do all that again. I'd mount the engine sideways to get the carb on the tank CL and forget all that hassle.

esamart...I have had 2 of my pumps stop working...not sure why, but 1 started pumping bubbles, and the other started dripping fuel out of the weep hole...

I have several pumps that are as old as they can be...from when they were introduced in the mid 70's (K&B backplate versions) and most still work great (I like 'em ) but both of them that "failed" did it suddenly.