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Inefficient piston

Unread postPosted: Wed Jun 04, 2008 10:36 am
Author: Biopyro
My piston doesn't have an o-ring and has a large-ish sized pilot volume 250cm^3 for a 1.5" valve, but according to GGDT it doesn't need reducing or a larger pilot valve (currently 1/2"). The thing is it seems very inefficient. When I fire there is a long blast of air through the pilot valve, often about 2-4x as long as in the video, which is aactually pretty good. I haven't used any sort of piston valve before, and it seems less powerful than my combustion.
Is this normal, is GGDT wrong about it or does my piston just need more optimisation?

Image

Unread postPosted: Wed Jun 04, 2008 11:05 am
Author: Carlman
yea there is definetly a big lag which is deacresing performance a bit.

try a modded sprinkler as pilot, or fill pilot volume with hot glue.

Unread postPosted: Wed Jun 04, 2008 1:36 pm
Author: MaxuS the 2nd
I go with the modded sprinkler valve as a pilot, a 1" version should do fine.
Shame even 1" versions cost $50 here instead of $5 over in good ol' america.

Unread postPosted: Wed Jun 04, 2008 2:25 pm
Author: jackssmirkingrevenge
The ideal pilot volume for a 100% efficient 1.5" piston shouldn't be more than 20cm<sup>3</sup>, I would look into ways of reducing that volume before increasing the pilot valve size.

Unread postPosted: Wed Jun 04, 2008 2:35 pm
Author: MrCrowley
I agree with JSR. Cut out a big piece of a kneeling board used for gardening, the foam ones, and use that as a bumper. They're quite thick so it gets rid off a lot of pilot volume.

Also check the tightness of the piston. How easy does it move inside the pipe? If you stuck it in 1.5" pipe and looked down the pipe, can you see much light coming from around the piston?

A 1/2" ball valve should be fine for this, but going bigger will improve performance.