check valve on OS91sz-h pumped

[Ghostrider]

After reading through the manual for the 91 sz-h pumped engine, it suggested (required) using a check valve if you want to run the engine on pump pressure alone (no exhaust pressure).

Is anyone doing it this way? or is there a better way?

If so, which check valve and where do you get it? :dontknow

[DavidH]

Most just vent the line from the tank to atmosphere. No check valve no filter.

Here is a picture.

http://www.helifreak.com/album_showpage.php?pic_id=6872


David

[HeliDan]

Hi Guys
This thread is not very clear on where the suggested check valve is installed. Also, does pumped mean that the engine uses an electric fuel pumped or it is bored out for more power?

What is the purpose of the check valve?

Thanx

[DavidH]

It says in the SZ Pumped instructions I believe. That a check valve can be use on the line that is vented to the atmosphere. I guess the reasoning behind that in the instructions is for people that worry that fuel would run out the line vented to the atomosphere when the model is in an orientation that would allow this.

The pump is pumping fuel from the tank. So there is positive pressure on the line that is vented to allow air to enter the tank. So no fuel will run out the line that I have seen. Most gas helis have open vents and they don't use check valves on the vent line.

The pump on the engine is operated by crankcase pressure from a nipple in the back plate. A running engine is just like an air compressor, it is pumping air pulses each stroke. So the pump is operated by the air pulses from the tap on the crankcase in the back plate.


David

[HeliDan]

Ahhhh. OK. Thanx............ Yeah, seems like the vacuum created by the fuel pump coupled with the atmospheric air pressure would not allow the leakage.

thanx for the lesson!! :D