Air Gun Home :: View topic - Plug-in 13XX Pump for a 2240

rsterne · Moderator

On one of the other Forums I frequent, somebody asked if you could convert a 13XX pump to work on a 2240 so that you could use it either with CO2 or as a pumper.... My first though was it was a crazy idea, but then I wondered WHY NOT !?!?!.... Over the last couple of days I converted my 1740 (a detuned 2240 with a 10" .177 barrel from a 1377) so that I had a pump I could just slide in, instead of the CO2 cartridge.... Here is a photo of the completed gun....

and here it is with the pump removed, back to being usable with CO2....

To install the pump only requires taking out the front trigger screw, unscrewing the CO2 end cap and dumping out the spent cartridge, sliding in the pump assembly, pressing it in to compress the O-ring which seals against the front of the 22XX valve, and installing a 3/8" long 8-32 high tensile screw in the front of the trigger group to retain the pump.... Part of the conversion was to replace the 6-40 22XX valve retaining screw on the bottom of the valve with a high-tensile, low profile, 8-32 SHCS to take the additional end force from the pump pressure, but that has no effect on the gun in CO2 use.... Instead of doing that, you could pin the valve with a couple of 8-32 setscrews, but you MUST locate the 22XX valve more securely for safety.... Here is the "business end" of the pump, showing the check valve and the #013 O-ring that seals the check valve housing to the end of the 22XX valve....

The 8-32 trigger screw is just hanging in the (unthreaded) hole for the photo, so don't think I tapped it crooked!.... The check valve assembly is retained in the end of the pump tube by two 1/8" long 8-32 setscrews at 120*, tapped into the 13XX tube and tightened into pockets in the brass check valve housing.... The heads are flush with the outside of the tube so that it can still slide into the inside of the 22XX tube.... It was necessary to turn down the OD of the pump tube slightly (about 0.010") so that it could slide into the 22XX tube, and shorten it of course.... The pump tube was shortened so that the end of it was about 1/4" past the end of the original trigger screw hole, but that distance may vary slightly from gun to gun and is quite critical.... Here are the details of the check valve.... First up is a photo of the parts....

The top part is the front end of a 13XX valve that has been faced off to work with a Flat-Topped Piston.... Below that is the check valve housing I made from the above, but I started with a Crosman replacement front housing because they come without the screw hole for the trigger screw.... That hole MAY be a problem, depending on how deep it is drilled, because the air inlet has to be drilled out to 7/64" for the check valve.... You can see that the three new pockets for the retaining screws are 1/4" further away from the O-ring.... This shortens the pump piston and the stroke by that amount, but is necessary to leave enough room for the check valve.... The check valve housing has been shortened to be flush with the end of the shortened 13XX pump tube.... The check valve itself is made from the shank and (thinned down) head of a 4-40 screw and a #006 O-ring which is a floppy fit on it and fits the inside of the 13XX valve nicely where the original check valve seated.... There is no spring on this check valve, but it works perfectly, just like the loose one in a male Foster fitting does.... The pump tube has been drilled and tapped 8-32 at 120* to the original trigger screw hole, which is not threaded.... Here are photos of the check valve itself....

There have been two recesses drilled into the shortened 13XX valve front to convert it into a check valve housing.... There is a 27/64" hole drilled 0.24" deep to clear the end of the 22XX valve housing.... Then there is a 14mm (just under 9/16") hole drilled 0.10" deep for the seat for the #013 O-ring which seals against the front of the 22X valve.... Here is the assembled check valve....

and here it is installed over the front of a 22XX valve.... It is not necessary to remove the piercing pin from the valve poppet, there is over 0.15" of clearance between the CO2 seal and the head of the check valve.... It is critical that you set the length from the trigger retaining screw to the #013 O-ring so that the O-ring is in considerable compression when first installed, and that you press hard on the pump before installing that screw and make sure it drops securely into the hole in the 13XX tube and the pocket in the check valve.... There is a lot of force once pressurized trying to drive the pump out of the end of the gun.... YOU HAVE BEEN WARNED !!! ....

It is necessary to have an adjustable Flat-Topped Piston because of the shortened pump stroke, but that is familiar to most so I didn't bother photographing it.... The 2289 pump handle I have hits the 2240 tube before closing completely, but it still latches over-center in the closed position so I haven't got around to fitting it yet.... You may decide to do that, and possibly even shave a bit off the top of the pump linkage as it hits the OD of the 2240 tube as well.... I didn't bother to do either, and I think it may be quieter this way because the metal of the pump linkage can't hit the tube on closing....

My test gun has been detuned with a smaller transfer port to stay under 500 fps in .177 cal to retain it's non-PAL status in Canada, so there is no point in talking about velocities.... However, I did examine the point at which the gun retains air.... With a stock 22XX hammer spring, it starts to retain air at 10 pumps, and with a 1377 hammer spring at 16 pumps.... My gun does, however, have a lightened hammer, which may affect that slightly, and it could be different in .22 cal as well, so you may be able to pump a bit more than that.... The 22XX valve spring is a bit stiffer than one in a 13XX valve, so that may affect the pressure at which air is retained as well....My gun equalled CO2 performance at 8 pumps, which acccording to my pumper spreadsheet is about 700-750 psi, so that would be consistent with other CO2 rifles running on HPA.... I have found that with a 1377 hammer spring, a 13XX typically starts retaining air at about 1500 psi.... I have based the safety calculations for this gun on that pressure, at which the end force on the valve and pump assembly is 356 lbs.... To withstand that force, with a 3:1 safety margin, REQUIRES that you replace the 2240 front trigger screw with a high tensile 8-32 SHCS that is 3/8" long, and that you EITHER replace the 6-40 screw that locates the 22XX valve with a high tensile, low profile 8-32 SHCS (requiring drilling and tapping the valve body) OR that you pin the valve with additional setscrews.... DO NOT ATTEMPT THIS BUILD WITHOUT ADDRESSING THE SAFETY ISSUES !!! .... I accept NO RESPONSIBILITY for your modifications, I'm only reporting what I did and the results....

Bob

AirGunEric · Site Admin

Bob, I think sometimes you do run out of things to stay amused with...

Very Happy

How long is the changeover time if someone were to want to swap from one configuration to the other?

rsterne · Moderator

Maybe a minute?.... More if you want to swap over the hammer spring....

Bob

rsterne · Moderator

Added note.... Something I didn't realize is that the internal volume of a 22XX valve with piercing pin is almost identical to that of a 13XX valve with the short check valve.... While the rear portion of the 22XX valve is larger ID, the 13XX valve has a much longer front cavity to hold the longer spring and check valve.... Add up all the space and take away the volume of the poppet, spring, and check valve or piercing pin, and it's pretty much a wash.... I'd always assumed the 22XX with it's large diameter, was larger volume.... It should therefore take the same number of pumps to develop the same pressure with either valve.... Since we are adding a very small amount of volume with the separate check valve chamber it might take one extra pump....

Bob

rsterne · Moderator

A quick glance at my Uber-Carbine shows that the idea of using a 2200 pump inside a 2250 tube might also work.... There are no holes in the 2200 tube forward of the transfer port, so there appears to be lots of length as the 2250 tube is only 1.5" longer than a 2240 tube....

Bob

Responsible Fun · New Member

WOW !!!! Now that there is a very talented and creative individual, this is yet another example of why I got back in to air guns...Just about anything is possible, I appreciate you sharing on how to do this conversion, but have you considered selling these conversions?
RF

rsterne · Moderator

Not going to happen, no time to do my own projects....

Bob

whm1974 · Veteran Member

Neat project, but given the cost of parts and time wouldn't be cheaper to buy both the 1377 and 2240? Or the 2289 and buy or make pistol panels for it?

rsterne · Moderator

Probably, but since when was this hobby about saving money or what makes sense?.... Mr. Green

I'd be far better off to drop $1000 on an AA 510 than do some of the crazy things I've done.... Shocked

Bob

whm1974 · Veteran Member

robert w · Senior Member

bob, you simply amaze me at the things you do to guns. you are a true gun genius and I have top respect for what you do. great job and I like it too Very Happy

bluespaghetti · New Member

Sincerely impressed