Airgun seals: Where are they?
by B.B. Pelletier
A new reader named Carl prompted today’s post. He owns a Daisy 22X and has some questions about oiling the seals. That resulted in this question:
You mention that you should keep your seals oiled. Where are these seals located?
I’ll do multi-pump pneumatics today and if there is interest, I’ll do the other types of airgun powerplants later.
Starting with the pump head
Think of a multi-pump gun as a progression of events. First, you pump air into the gun’s reservoir. That takes a pump head that can seal air against loss as it compresses it into a small space. The pump head is a pliable material that fits the inside of the pump tube tightly enough to compress air but loosely enough to move easily. The pump head usually swells from increasing air pressure. In some guns, there’s an O-ring, like a piston ring, around the head very near the end. Oil on the contacting surfaces of either the O-ring or end of the pump head seals the air in front of the head, just as oil in your car engine helps the piston rings seal the explosive gasses of combustion.
This rough diagram shows the relative locations of the seals in a multi-pump.
The inlet valve
As the pump head compresses air, the inlet valve in the end of the reservoir is forced open by air pressure. Air passes into the reservoir, which in most multi-pumps is nothing more than empty space inside the valve body. It doesn’t take much air to drive a pellet! When the pump stroke is complete, the inlet valve’s return spring closes the valve. As the reservoir pressure increases, more pressure is needed to open the inlet valve, so the pump head travels farther before the inlet valve opens. You feel the increased pressure as feedback in the pump stroke.
The exhaust valve
Air remains in the reservoir/valve until released through the exhaust valve. Typically, a spring-driven weight called a hammer knocks the exhaust valve off its seat, releasing the air. The released air flows through the same tunnel the valve stem operates in, but a hole in the side of this tunnel lets the air escape up to the barrel, where it gets behind the pellet. The bolt that loaded the pellet has an O-ring seal on it, so the only way the air can escape is to push the pellet out of the way.
Pump tube to barrel seal
This just keeps the air sealed inside the tunnel so it has to push the pellet out of the way.
Oiling all the seals
When you oil the pump head, oil migrates through the gun with the compressed air. By oiling this one spot, you are oiling the entire airgun.