350psi on 150psi rated sliding valve and 150psi rated QEV.

[ham_machine]

I have spent quite a few days looking through the web at different QEV's, for any alternatives or recommendations. I do not want to build one, I would like to buy one. However, from what I have seen for sale on the internet, most of the QEV's have very low pressure ratings for what I want. I will be using 350psi (which is quite a bit more than the 150psi rated valve).

I understand that some people have put these valves way beyond their pressure rating, (they have used them up to 600psi). Now I want to know whether or not this is a silly thing to do, has anyone had any experience with this? Surely It has a 150psi rating for a reason? I am always extremely cautious with pressure.

I read on another topic that it is better to use a milled QEV than a cast one. Does anybody else agree with this? Most of them are from hongkong/china, so look a bit dodgy in the quality. My main concern is safety, I have built a 350psi cannon before, but never used a QEV.

This subject may have been mentioned before, but with the high pressures - there are no second chances, and that is why I want to guarantee my safety first my asking anyone out there with experience.

[fenrir]

It's ok to use 350 psi. The worst thing that could happen would be the diaphram getting blown out.

[ham_machine]

It's ok to use 350 psi. The worst thing that could happen would be the diaphram getting blown out.

Do you think it will be safe to use a sliding valve to pressures of 350psi?

sliding valve.jpg (51.16 KiB) Viewed 3630 times

[ham_machine]

Does anybody out there think it is safe using 350psi on a 150psi rated sliding valve, or on a 150psi rated QEV? Increasing the pressure will no doubt decrease the lifespan. I heard the diaphragm will fail first on the qev. What about the sliding valve?

Will there be any leakages on either of these, if I were to use 350psi??

I want my gun to work at 500psi, so I know it will work safely at 350psi.

Please write whether it is safe or not, so I can decide if I will use it.

Sliding valve - rated at 150psi

sliding valve.jpg (51.16 KiB) Viewed 3656 times

Qev - rated at 150psi

qev1.JPG (77.75 KiB) Viewed 3656 times

[Ianbuckwell]

I use around 300psi on a QEV made by Parker rated at 100-150psi(can't remember which) and it has been absolutely fine, I took it apart as thought I had killed it, but found it was my fault as a blob of solder had gotten into it stopping it from sealing, I checked the rubber diaphragm and it was in perfect condition. I have a cheap blue Chinese slide valve from Ebay and its worked fine apart from once when an o ring partially came out, but if I remember correctly this was when I accidentally went over 300psi by a fair bit. I guess quality and tolerances vary between items and manufacturers so when first using them I started off at around 100psi and slowly increased as I became more confident, I wouldn't say it was safe to do this and may be a good idea to wear eye protection as at the end of the day you are using pressures higher than the items are rated at so better safe than sorry.

[Zeus]

I've taken that style of QEV, a 1/4" one, up to 700PSI, at least 100 times now. It'll be fine. I've taken a few of the square QEVs in 1/2" up to the same a few hundred times, no failures at all. Slide valves are very low wear items, the O rings aren't exposed to large areas of pressure, keep them lubricated with an O-ring safe lubricant (remember oil and silicone lube destroys latex kids ), and you'll be fine.

I swear we have these 'can I use my QEV at x pressure' threads every few months.

[wyz2285]

I swear we have these 'can I use my QEV at x pressure' threads every few months.

You mean every few week or day, the fact we have two active thread about the same matter at the moment It's good people nowadays worry about pressure ratings but back in my day, I just test it myself

[Brian the brain]

I merged the two identical topics...


and by the way..The QEV should work above it's rating.
However...with a projectile in the barrel, a piston failure will result in an unexpected launch.
Not pretty.

The slidevalve might seeze up under the extra load making it impossible to move by hand.

[ham_machine]

Thanks guys for the feedback! Think I will take the risk and use 350psi. Has anyone ever experienced a QEV failing, when the diaphragm blows out?

[Brian the brain]

Not me personally..I have had a pilotvalve develop a leak resulting in an unintended launch.

I believe it is quite common among British spudders to add a ballvalve between the QEv and the barrel as a safety.