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Let’s take it apart

The Aquamatic 425 Valve


Aquamatic 425In 1998 or so, there was Spud Gun MkI. There are very few surviving pictures of it and even fewer of it in action. It was built wholly of 2″ PVC pipe. Two 10′ joints made up the tank; the barrel was a single 10′ piece. A 1/4-turn ball valve controlled the firing and it was sticky and hard to turn. More important, the person firing the gun was so occupied with turning the valve that they couldn’t watch the spud fly. MkII needed some sort of quick-action big-bore remotely-triggered valve. Several years ago browsing through Mendelson’s in Dayton, this beauty was staring at me from a shelf. I bit.

It was painted with three or four coats of ugly cafeteria-green paint. I stripped it and put a coat of primer and safety yellow on it. I also plumbed it up with a MAC electrically operated valve and a gauge. Until today, it had never been fired. After some less-than-spectacular firing, I tore it down to make sure the piston hadn’t rusted in place. These are the photos. Also included, photos of firing.

This is what she looks like all together. The 2″ union near the bottom of the photo connects to two 2″x10′ tanks. The yellow-handled valve and the quick connect air fitting are the means to pressurize the whole affair. The blue box on top of the big yellow mass is the electrically operated valve which controls the larger valve. The copper tube keeps the topside of the diaphragm pressurized as well as provides pressure to operate the piston in the blue valve. The olive colored gizmo with the ball-chain is a MIL spec connector to power the electrical portion of the blue valve.

Aquamatic 425

Removing the six bolts from the valve allows removal of the top and access to the diaphragm. This area is normally pressurized to the same pressure that the valve is closed against. Because the surface area up here is larger than the area of the piston against the fluid the valve is closed against, this side wins the push and shove and keeps the valve closed. The tiny hole in the shaft in the middle of the brass-colored plate goes all the way through into the pressurized side of the valve.

Aquamatic 425

The shaft is slotted so that one may use a screwdriver to keep the whole affair from turning as one takes the nut off.

Aquamatic 425

Lefty-loosie and off the diaphragm comes. With an appropriately sized socket, one can remove the brass seat and take the entire piston out. Notice that there is a copper gasket on the shaft. If you can’t see it, take my word. It is supposed to be there. It goes between the diaphragm and a shoulder on the shaft to seal it. I mistakenly positioned in on the top side when I reassembled the valve the first time and it had a slow leak. Also worth note, this bottom cavity has a port to the outside world just like the top. It allows air to come and go as the diaphragm moves. It is threaded so I suspect one could use it to pressurize the bottom side to hasten opening. That is the plan for the MkIII.

Aquamatic 425

With the seat out, the piston can come out. There are two O-rings in the hole through the seat, so don’t miss noticing those. They’re important for a good seal and smooth operation.

Aquamatic 425

This is the valve stripped of all of its moving parts. The barrel, by the way, screws onto the right end in this photo.

Aquamatic 425

I promised pictures of the valve in action. The target is an unsealed gallon jug of water at close range. The projectile is a frozen potato of 2″ diameter and roughly 3″ in length. Pressure was somewhere in the area of 105psi.

Pre Boom

The top of the stool was cracked from the force of the water exploding against it. There were no pieces of potato remaining worth note. Remains of the jug can be seen in midair just behind the bush.

Post Boom

Yes, sometime I will get video instead of just stills.

posted under BlowItUp, TakeItApart

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