More Hw90 Help Required

[Hartcliffer]

Hi all,

After buying a decidedly underpowered Hw90, I decided to strip it down, replace the seals and valve, and re-assemble. Everything went well, pumped it up (to 10 bar), only to find that I couldn't cock it. Thinking that I had overfilled it, I tried to let some air out, only for ALL the air to escape. Filled to 5 bar, rifle would cock, but when fired, all the air would escape. Filled again to 10 bar, same issue. Am I missing something here? Feels like I've done something wrong, although I do find it odd that when trying to let some air out, the valve stays open and it all leaves....

[bighit]

Hi all,

After buying a decidedly underpowered Hw90, I decided to strip it down, replace the seals and valve, and re-assemble. Everything went well, pumped it up (to 10 bar), only to find that I couldn't cock it. Thinking that I had overfilled it, I tried to let some air out, only for ALL the air to escape. Filled to 5 bar, rifle would cock, but when fired, all the air would escape. Filled again to 10 bar, same issue. Am I missing something here? Feels like I've done something wrong, although I do find it odd that when trying to let some air out, the valve stays open and it all leaves....

did you just tap the valve or hold it in?

you are supposed to just give it a sharp tap . possibly your valve is sticky .

[Benelli B76]

Hi all,

After buying a decidedly underpowered Hw90, I decided to strip it down, replace the seals and valve, and re-assemble. Everything went well, pumped it up (to 10 bar), only to find that I couldn't cock it. Thinking that I had overfilled it, I tried to let some air out, only for ALL the air to escape. Filled to 5 bar, rifle would cock, but when fired, all the air would escape. Filled again to 10 bar, same issue. Am I missing something here? Feels like I've done something wrong, although I do find it odd that when trying to let some air out, the valve stays open and it all leaves....

Pity you decided to re-seal it. If you had just topped up the ram pressure it would have probably been fine. They do tend to leak over years, I have topped up a few in the last few months. Firing should not release any air from the sealed unit, the seals or valve must leaking again somehow.

Baz

[Hartcliffer]

did you just tap the valve or hold it in?

you are supposed to just give it a sharp tap . possibly your valve is sticky .

If I'm honest I don't think that I did a sharp tap, but it is a brand new valve. I'll give it another go in the morning, and if that doesn't work I'll strip it down again. I really want it to be right, as I do like the way it feels.

[bighit]

If I'm honest I don't think that I did a sharp tap, but it is a brand new valve. I'll give it another go in the morning, and if that doesn't work I'll strip it down again. I really want it to be right, as I do like the way it feels.

they say a sharp tap in the theoben and hw90 pump instructions not sure why it wont cock though. there is lots of answers about how much pressure it should be .

i have never had mine stripped . what pump are you using to pump it up? could the pump be inaccurate ?

i topped mu evolution up and chronoed it .i have the slim jim pump with no gauge on it .

[Benelli B76]

It is hard to read the pressure on the gauge as it is so low. When I have topped rifles up it seems to read about 350 p.s.i. On a .22 I normally have to tap the valve lightly to release a little pressure to get 11.4 ft.lb. A tiny release or air pressure can make a huge difference in power on the HW 90.


bAZ

[NTSOG]

Hi,

One of my old Theoben Beeman/HW 90s was cocking intermittently. The problem turned out to be serious wear through the pin at the front pivot point and also wear in the hole through which the pin fits. I had to replace the whole cocking lever and pin. Essentially I could not move the cylinder far enough rearwards to engage and cock the rifle. Now all is well.

Jim

via Ballarat
Australia

[bighit]

It is hard to read the pressure on the gauge as it is so low. When I have topped rifles up it seems to read about 350 p.s.i. On a .22 I normally have to tap the valve lightly to release a little pressure to get 11.4 ft.lb. A tiny release or air pressure can make a huge difference in power on the HW 90.


bAZ

some people are using suspension shock pumps from mountain bikes
https://www.tredz.co.uk/.RockShox-Hi...0aAlDWEALw_wcB

so unless its a top end branded one the gauge may read wrong.

if using a pcp tank to fill i dare say it would be hard to stop it blowing a seal if you let too much air rush in . having never used a pcp tank to pump one up i may be wrong. using a hills type pcp pump would be safer for me anyway.


according to a post on here in 2006 the hw90 needs to be pumped up to 17bar . which is around 260 psi

http://www.airgunbbs.com/showthread....-gas-ram/page2

but i have heard loads of different pressures being mentioned .

[Hartcliffer]

Thanks for all your input guys, it's much appreciated.

The pump I've been using is a Bay special, which has worked fine with my HPA XS79, although with that I've always gone by the gauge on the bottle and not on the pump. Maybe you're right about the gauge being messed up. I'll give it another go tomorrow I think.

[10/10]

Make sure the cocking arm is in the correct spot in the piston and then you have to Re set the safety catch before you replace the trigger guard
Ive just done mine

[stagmanv835]

you have to Re set the safety catch before you replace the trigger guard
Ive just done mine

that had me scratching my head for an hour or three a few years back

[Benelli B76]

some people are using suspension shock pumps from mountain bikes
https://www.tredz.co.uk/.RockShox-Hi...0aAlDWEALw_wcB

so unless its a top end branded one the gauge may read wrong.

if using a pcp tank to fill i dare say it would be hard to stop it blowing a seal if you let too much air rush in . having never used a pcp tank to pump one up i may be wrong. using a hills type pcp pump would be safer for me anyway.


according to a post on here in 2006 the hw90 needs to be pumped up to 17bar . which is around 260 psi

http://www.airgunbbs.com/showthread....-gas-ram/page2

but i have heard loads of different pressures being mentioned .

The initial pressure you pump to is not critical as long as it is not too high to cock the rifle or damage the seals. It is very unlikely you are going to get exactly the power level you want without tapping the valve to release a bit of air. If you put too much in at your first try the 90 will be almost impossible to cock. I use a Hills pump.


Baz

[Hartcliffer]

Given it another go, and still no joy. I think that this one is beyond my abilities, and I don't want to mess it up anymore. Just have to decide if I want to sell it as spares or repair, or break it up for parts. I've got too many others that need work on, work which I'm capable of and have done before, so I think I might just cut my losses on this one. If anyone's interested, let me know.

[air-tech]

Never taken mine apart - Question - is any of the dynamic sealing O-ring based? If so - O ring sizing can be critical. Similarly, it is easy to damage an O ring when being fitted. End of the day, the leak is seal related so a very close inspection ought to reveal the problem, assuming they were correctly sized.

[Shed tuner]

Yes Karl, the main ram seal is an o- ring, and yes, sizing is critical. Nb it also has a delrin backer.