Difference between revisions of "Piston valve"
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| − | A piston valve is a [[pilot valve|pilot]] | + | A '''piston valve''' is a [[pilot valve|pilot]] operated valve. It is very similar to a [[diaphragm valve]] in therory, but replaces it's flexable diaphram with a rigid cylinder. There are 2 varieties; barrel sealing and chamber sealing. |
== Construction, barrel sealing == | == Construction, barrel sealing == | ||
| − | The piston is often a well fitting cup-shaped object, such as a endcap. To provide a sealing face, a peice of rubber is attached, typicaly with a bolt. | + | The piston is often a well fitting cup-shaped object, such as a endcap. To provide a sealing face, a peice of rubber is attached, typicaly with a bolt. Equalization is accomplished by simply allowing the air to leak past the piston and into the chamber. Some people will machine their own pistons, in which case they often build [[O-ring]]s into them. With the O-rings, you need to make a small equalization hole; sometimes this is fancied up to be a homemade [[check valve]]. |
| − | Because a piston is heavier and harder than a | + | Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recomended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labled "<b>F</b>" in the "use, barrel sealing" diagram. |
| − | These valves are often used on [[coaxial]]s and [[over/under]]s. In an over/under, the valve is built in a "T" fitting. The barrel is put | + | These valves are often used on [[coaxial]]s and [[over/under]]s. In an over/under, the valve is built in a "T" fitting. The barrel is put coaxially through one end, the pilot and piston are put in the opposite one, and a chamber is connected to the perpendicular opening with a 90° elbow. |
== Use, barrel sealing == | == Use, barrel sealing == | ||
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Opperation: | Opperation: | ||
<ol><li>Air is added by filling behind the piston (C). | <ol><li>Air is added by filling behind the piston (C). | ||
| − | <li>The piston (E) slides forwards, and seals | + | <li>The piston (E) slides forwards, and seals against the barrel (A). |
| − | <li>More air is added, and leaks around the piston (or through a small | + | <li>More air is added, and leaks around the piston (or through a small equalization hole) and into the chamber (B), filling it to the desired pressure. |
| − | <li>The pilot valve (D) behind the piston is | + | <li>The pilot valve (D) behind the piston is opened, the pressure in the [[pilot|pilot volume]] (C) drops, and the higher pressure in the chamber area pushes the piston away from the barrel. |
<li>The air flows around from the chamber, and into the barrel, propelling the projectile.</ol> | <li>The air flows around from the chamber, and into the barrel, propelling the projectile.</ol> | ||
| − | The | + | The performance of these valves can be calculated with the [[GGDT]]. |
If your valve [[honking|honks]], it is probably a good idea to invest in a better [[pilot valve]]. | If your valve [[honking|honks]], it is probably a good idea to invest in a better [[pilot valve]]. | ||
[[category:valves]] | [[category:valves]] | ||
Revision as of 07:54, 26 October 2005
A piston valve is a pilot operated valve. It is very similar to a diaphragm valve in therory, but replaces it's flexable diaphram with a rigid cylinder. There are 2 varieties; barrel sealing and chamber sealing.
Construction, barrel sealing
The piston is often a well fitting cup-shaped object, such as a endcap. To provide a sealing face, a peice of rubber is attached, typicaly with a bolt. Equalization is accomplished by simply allowing the air to leak past the piston and into the chamber. Some people will machine their own pistons, in which case they often build O-rings into them. With the O-rings, you need to make a small equalization hole; sometimes this is fancied up to be a homemade check valve.
Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recomended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labled "F" in the "use, barrel sealing" diagram.
These valves are often used on coaxials and over/unders. In an over/under, the valve is built in a "T" fitting. The barrel is put coaxially through one end, the pilot and piston are put in the opposite one, and a chamber is connected to the perpendicular opening with a 90° elbow.
Use, barrel sealing
Opperation:
- Air is added by filling behind the piston (C).
- The piston (E) slides forwards, and seals against the barrel (A).
- More air is added, and leaks around the piston (or through a small equalization hole) and into the chamber (B), filling it to the desired pressure.
- The pilot valve (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the barrel.
- The air flows around from the chamber, and into the barrel, propelling the projectile.
The performance of these valves can be calculated with the GGDT. If your valve honks, it is probably a good idea to invest in a better pilot valve.
