It's a balanced valve and the adjustment is for the balance chamber volume. The spring tension is irrelevant here, the maker of the video has misunderstood the operating principle. The chamber volume defines the point when the valve actually starts to close as the chamber pressure meets the throat pressure and pressurized air starts acting against the valve stem area that's open to atmosphere.
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the Daily hi thread
Making of a Exhaust Valve
- Thread starter 1260engineer
- Start date
It's a balanced valve and the adjustment is for the balance chamber volume. The spring tension is irrelevant here, the maker of the video has misunderstood the operating principle. The chamber volume defines the point when the valve actually starts to close as the chamber pressure meets the throat pressure and pressurized air starts acting against the valve stem area that's open to atmosphere.
Tricky-Dicky
Member Extraordinaire
For 12 fpe you can adjust the valve for short dwell with fast open and close, ideal for reduced air usage. For high power you can adjust for long dwell and fast open and slower close. The main point of balanced valves is much reduced force that holds the valve shut, due to that chamber that's open to atmosphere. That's what allows fast open with small strike that ssg provides. The closing then is defined by how fast the chamber fills with high pressure air.
Tricky-Dicky
Member Extraordinaire
1260engineer
Member Extraordinaire
My Titan's have restricted hammer and EV valve and are adjustable on both. there also sub 12's
1260engineer
Member Extraordinaire
Hello mate
you might want to look at that( The main point of balanced valves is much reduced force that holds the valve shut, due to that chamber that's open to atmosphere )
again as the pressure that holds the EV shut is the charge that powers the pellet . the pressure after a reg is determined by the reg . the volume is determined by the plenum. what ever the volume of the plenume the pressure is still the same .
on a none regulated rifle you can change the pressure on the valve by making its surface area smaller .
Hello mate
( The main point of balanced valves is much reduced force that holds the valve shut, due to that chamber that's open to atmosphere )
again as the pressure that holds the EV shut is the charge that powers the pellet . the pressure after a reg is determined by the reg . the volume is determined by the plenum. what ever the volume of the plenume the pressure is still the same .
on a none regulated rifle you can change the pressure on the valve by making its surface area smaller .
English is not my first language so here's some proper talk about balanced valves and how they work. The model in the video is also presented. https://www.gatewaytoairguns.org/GTA/index.php?topic=152413.0
1260engineer
Member Extraordinaire
Ive seen them before mate . the reason they didn't catch on was there over complicated and the HPA acting on the valve piston actually acts as a break .
The simplest way to drop the pressure on the valve and allow it to close easier is to create a slack tide . ie back pressure.
without giving to much away the chamber behind the valve acts like a mini plenum which equals the volume of pressure for the shot this then leads to the transfere port . the dimensions of the port being smaller stops the air for a split second. at this point the air in the plenum chamber and the chamber become balanced. this allows the exhast valve spring to close the valve .
a cleverly set up ftp900 can do the same thing using the throat screws to create back pressure.
I agree about them being complicated. In addition the o-ring under pressure against the poppet (or wherever it's used) is not good for small fps spread. Balanced valves are mostly used in bigbores with large valve throat where opening the valve requires really stiff hammer springs. American Air Arms has been using them in their guns but I didn't know about this Epic, it will be interesting to see how the concept works on low power guns that get shot a lot. Yes, I know about restricted inlet valve chambers - although I've never thought about using one for the purpose you stated. Interesting idea
Tricky-Dicky
Member Extraordinaire
So basically the physical size of the area of the back of the valve is the key point in how easy/difficult it is to open/close rather than the volume of air?
So the adjustable volume of the Epic is not going to be the main factor in how the valve behaves.
So the adjustable volume of the Epic is not going to be the main factor in how the valve behaves.
1260engineer
Member Extraordinaire
I use massive exhaust valves compared to normal sub 12 rifles . 12mm diameter with a seal edge at 11mmI agree about them being complicated. In addition the o-ring under pressure against the poppet (or wherever it's used) is not good for small fps spread. Balanced valves are mostly used in bigbores with large valve throat where opening the valve requires really stiff hammer springs. American Air Arms has been using them in their guns but I didn't know about this Epic, it will be interesting to see how the concept works on low power guns that get shot a lot. Yes, I know about restricted inlet valve chambers - although I've never thought about using one for the purpose you stated. Interesting idea
just the shafts without the seals .
And i use light weight titanium hammers
the T2 has a 3 piece EV as i was experimenting with different shaped valve seals . i got the seal shape right to help open the valve . then as the pressure balanced at slack tide it closes . because of the surface area of the valve and it only opening 0.75 of a mill it has a very fast cycle time .
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El Caro
Super member
A good example is a high power .72" pcp rifle which is quite popular over the pond. There was a review of one on Youtube where all of the air reservoir was unintentionally used on one shot causing significant recoil
. This was quickly glossed over but is a fault caused by the system not behaving itself
. Bowkett used to use the system based on backpressure but to rapidly open the valve with little effort where all the air needs to be released such as his high power pump ups. The example on Youtube behaved like that unintentionally. They can be very sensitive to set up apparently adding more complexity into the pcp mix
A good example is a high power .72" pcp rifle which is quite popular over the pond. There was a review of one on Youtube where all of the air reservoir was unintentionally used on one shot causing significant recoil
On high power guns I have had really good results with PEEK poppet and 2mm valve stem. The PEEK being less elastic it's easy to knock open and with 2mm stem the closing force is greatly reduced giving long dwell with rather soft hammer spring. I have some PEI (Polyetherimide) bar waiting to become a poppet for my .45 Evanix, that should be even better than PEEK.
OMG please can you replicate some of the knock off valves for the early Brummie Webley Raiders 
Absolute weak point on these otherwise fine guns for their time, and seem to be as rare as unicorn droppings!
The fill valve was no better but at least these can be obtained in upgraded form in brass with a sealing O ring
I've scoured everywhere trying to find a replacement
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Absolute weak point on these otherwise fine guns for their time, and seem to be as rare as unicorn droppings!
The fill valve was no better but at least these can be obtained in upgraded form in brass with a sealing O ring
I've scoured everywhere trying to find a replacement
Webley raider two shot exhaust valve
Hi gang anyone have capability of making up exhaust valves if I can supply dimensions or the old valve stem as a pattern??? Have had this thing apart numerous times now and have come to the conclusion the nylon head is either porous or gone brittle with age and no matter what despite lapping...
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