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Unread postPosted: Mon Mar 21, 2011 9:41 am
Author: Hotwired
It just means a piston that when opened, shows significantly more surface area than when closed, resulting in the piston opening faster once slightly opened.

Unread postPosted: Mon Mar 21, 2011 9:48 am
Author: Crna Legija
its a piston with a big part and a small part, you only need a little bit to get it to move but once it start it open up tonnes more surface area and makes the piston really POP open. you can see it in jsr drawing above look how little the pressure can act on at the start.

edit to late :(

Unread postPosted: Mon Mar 21, 2011 9:51 am
Author: Gun Freak
Ok thanks, makes sense. :)

Unread postPosted: Mon Mar 21, 2011 11:39 am
Author: jackssmirkingrevenge
For the sake of clarity:

Unread postPosted: Fri Sep 09, 2011 10:29 am
Author: jackssmirkingrevenge
Thinking of giving this another go, now that I have more experience with materials and machining. The delrin/metal face seal is quite common in the commercial PCP airgun field, the question is how well it can stand up to the heat spike from hybrid ignition.

This would naturally be filled by placing the cartridge inside a filling chamber.

Unread postPosted: Fri Sep 09, 2011 10:55 am
Author: Labtecpower
Looks good!

How are you going to force th piston forward? pneumatical or with a spring?

Unread postPosted: Fri Sep 09, 2011 11:00 am
Author: Moonbogg
Looks like a fun project. I also wonder how the delrin would do. So many plastics to choose from for piston material.

Unread postPosted: Fri Sep 09, 2011 11:03 am
Author: qwerty
How are you going to force th piston forward? pneumatical or with a spring?


Piston goes backward with the pressure spike of the mix igniting.

Shame i don't use my hybrid much anymore, too much fuss cutting out stupid burst disks, might have to try a piston hybrid.

Unread postPosted: Fri Sep 09, 2011 11:04 am
Author: dewey-1
Moonbogg wrote:Looks like a fun project. I also wonder how the delrin would do. So many plastics to choose from for piston material.


Delrin is so nice to machine compared to some of the other plastics.

Unread postPosted: Fri Sep 09, 2011 11:43 am
Author: Labtecpower
Piston goes backward with the pressure spike of the mix igniting.


I know, but how is it held against the barrel?

Unread postPosted: Fri Sep 09, 2011 11:50 am
Author: jackssmirkingrevenge
Labtecpower wrote:How are you going to force th piston forward? pneumatical or with a spring?


No springs, just the pre ignition pressure. The idea is that it is placed in a fill rig as attached, fuel is injected and the rig is sealed. The rig is taken up to pressure, then the schrader stem is depressed, causing a pressure imbalance which should force the piston shut.

dewey-1 wrote:Delrin is so nice to machine compared to some of the other plastics.


So true, it's become my favourite polymer :) and quite cheap too!

Unread postPosted: Fri Sep 09, 2011 11:59 am
Author: dewey-1
JSR;

Use 2 set screws rather than an exposed headed screw!

Unread postPosted: Fri Sep 09, 2011 12:05 pm
Author: jackssmirkingrevenge
dewey-1 wrote:Use 2 set screws rather than an exposed headed screw!


This would be just to fill the cartridges at pressures below 400 psi, so it doesn't to be neat or overengineered.

Unread postPosted: Fri Sep 09, 2011 12:28 pm
Author: dewey-1
jackssmirkingrevenge wrote:
dewey-1 wrote:Use 2 set screws rather than an exposed headed screw!


This would be just to fill the cartridges at pressures below 400 psi, so it doesn't to be neat or overengineered.


My apologies then!

I did not realize that was the filling rig. :)

Unread postPosted: Fri Sep 09, 2011 1:26 pm
Author: Labtecpower
JSR wrote:No springs, just the pre ignition pressure. The idea is that it is placed in a fill rig as attached, fuel is injected and the rig is sealed. The rig is taken up to pressure, then the schrader stem is depressed, causing a pressure imbalance which should force the piston shut.


Why would this work?

If you inject the mix, it will push back the piston.
Why would there go enough mix behind the piston to force it shut when you depress the schrader?

I think it would slam against the back plug while filling, removing the air behind it.