I’ve been discussing QEV cannons with Dustin recently and talking about how to safe the system without firing. There is a diagram out there that shows how to do this with a 5-way valve, which is expensive and complicated to set up right. It works, but the diagram below is a simpler set up using a 3-way valve and a check valve. So for those few that use QEV cannons: Valve 1 - Two position, 3-way toggle (SMTV-3, FTV-3, MTV-3, TV-3S, etc.) Valve 2 - Normally open, 3-way (MAVO-3, SMAV-3, EVO-3-XX-XX, etc.) Valve 3 - Quick exhaust (JEV-F2M2, etc) Check 1 & 2 - One-way check valve (MCV -1, etc.) Operation: •When Valve 1 is in the off position, the flow from the regulator is blocked and the entire cannon system down stream is depressurized through the valve exhaust port. When Valve 1 is opened the cannon system pressurizes. •Valve 2 is the firing valve. When Valve 2 is open (normal position) the accumulator charges. When the valve is closed (firing position), the output is vented and the quick exhaust valve opens. •Valve 3 dumps the accumulator into the gun barrel when opened. It opens when then inlet pressure from Valve 2 is lower than the accumulator pressure. As long as the inlet pressure is higher than the accumulator pressure, Valve 3 stays closed, which is key to venting the system without firing. •The vent line allows the accumulator to be depressurized without opening the quick exhaust valve. Check 1 prevents the quick exhaust valve from opening when Valve 1 vents pressure, by keeping pressure high between Check 1 and Valve 3. Check 2 is optional: it conserves gas by preventing the accumulator from filling (and gas flowing out the gun barrel) when Valve 2 is closed (firing position). You can down load this information in a PDF attached to this post
RE: Quick exhaust valve cannon set up Thanks for sharing this Mark. This really simplifies things for ships with mixed positive/negative pressure weapons.
That's how it's done, all right. Many people forget about the vent line and check valve #2, until they "safe" their guns and get shot in unspeakable places. Every successful ship I've seen with negative pressure cannons either started with that layout or switched to it very quickly.
Can any of you remember seeing any kind of fitting that could rotate under pressure, and has two lines passing through it? If not, can you conceive of a way to produce one? I had an idea, but I don't think I could make it well enough, or keep it in line with the sizes of fittings we currently use. In case yer a wunderin' it is to serve as part of a gas passage through a centrally located rotation king pin for a canister gun that busted into my daydreams last week.
Check out Parker fittings and their Prestolok series. They have all sorts of push-to-connect swivel fittings
