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Aluminum Flat Top Valve & Piston Kit
For Crosman 1322 1377 2289 P1322 P1377

MAY 2021 UPDATE: The piston now features two o-rings for better compression. Looks a lot more professional, too.

MAY 2021 UPDATE x2: A solid brass piston is now available. It's fancier. It's heavier. It's bling that only you know is inside...?

APRIL 2023 UPDATE: Crosman 362 Flat Man's Pack now available.

APRIL 2023 UPDATE x2: Adjustable Pistons now available.

  • The Flat Top upgrades are immensely popular with Crosman pumper enthusiasts. The idea is that by giving the gun a larger air reservoir, you can do more work per pump, resulting in the same shot velocity with FEWER pumps. Or, increase velocity with the same number of pumps over OEM.
  • You can buy just the Flat Top Valve, just the Piston or the Complete Kit.
  • Note that you should not install just a Flat Piston with an OEM valve. The gun won't cock completely and will be useless.
  • You can, however, install just the Valve.
  • But the smart move is to install the complete kit.
  • Want even more mods? Consider the Flat Man's Pack, which is the Flat Top Kit + Power Spring + Max Flow Bushing.
  • The Flat Top Valve is an OEM Crosman valve that has been heavily modified.
  • First, we put it on the mill and angle the exhaust so the escaping air doesn't have to make a hard 90 exit.
  • After that, we straighten up the exhaust hole with a nice six-fluted bit.
  • Then, we flatten the face to allow more air to be pressurized per pump.
  • Finally, we remove as many machining marks as we can to make a perfectly smooth exterior.
  • And, of course, the valve is cleaned and polished prior to reassembly with BRAND NEW o-rings.

aluminum flat valve

brass flat valve

  • This is the Flat Top Piston. It is 7075 aluminum milled from scratch. A solid brass version is available, too.

This is the older single o-ring style. All shipments will feature double o-ring pistons as shown below.

  • And here is the complete kit.


Full Kit

Install Video

  • Here is the kit with the brass piston.

Brass Piston


13xx / 2289 Flat Top Kit
$69.99 - $99.99

Not compatible with the 362, whose kit is here.

Flat Valve Only
$34.99 - $49.99

Flat Piston Only
$39.99 - $49.99

While you can buy the valve-only and piston-only individually, they're not designed
to be used with competitor's products, nor will they work with non-flat parts.

The Flat Valve won't work with an OEM Piston and vise versa.

But, they are available, if you have a specific project you want to accomplish.