2289 Valve

[rsterne]

Although the extra volume of air would, in theory, take longer to dump.... at the same number of pumps the pressure inside the valve will be less.... The critical factor in how long/far the valve opens is the air pressure operating against it.... so in fact the valve will have an easier job dumping the same number of pumps with a valve of larger volume.... What you will find, in fact, is that at low pump numbers the gun will actually lose velocity because pressure is more important than volume.... As you pump more and it gets harder and harder to pack the air into the valve, then the larger volume will pay benefits....

I just rebuilt a Crosman 1400 (large swept volume on the pump, about twice that of a 2289).... There was a spacer inside the valve taking up about half the volume.... Removing that spacer lost velocity at 4 pumps or less, broke even at 5 pumps, and gained velocity at 6 pumps or more.... On my "Uber-Pumper" I found that increasing the valve volume only paid benefits at over 10 pumps.... I achieved 900 fps with 14.3 gr. pellets eventually.... but quickly grew tired of pumping it....

Bob

[Doc Sharptail]

.... but quickly grew tired of pumping it....
Bob

I didn't think I was ever going to see an admission like that from you. Things always change-up, though

I've melted a delrin piston, or six, trying to force the 13-XX beyond what it's designed for. It can be done. It's my opinion that the current crop of aluminum 13-XX valves are poor candidates for volume expansion via the boring and cutting method. A thread-in spacer between the valve halves would be a stronger solution- at the cost of swept volume. A longer pump tube pretty well becomes a prerequisite...

Regards,

Doc Sharptail

[rsterne]

You mean like this?....



That was the valve from my .22 Uber-Pumper which used a 1400 pump tube and linkage.... I reached 902 fps with 14.3 gr. JSB Express pellets (26 FPE) at 22 pumps.... but only after I replaced the F-T-P piston with aluminum.... The Delrin one melted severly.... The gun was starting to retain air at 20 pumps, and at the time I was running a 2200 hammer spring.... Had I had a Disco spring, even more performance might have been possible.... but MAN that thing was a bear to pump at 20+ pumps....

Bob