rocket launcher slide valve assembly
  1. Check the orientation of the slide valve.  I’ve installed this valve backwards a couple of times myself.  Make sure the hexagonal end is closest to the launcher.
  2. Leak in the bike pump.  When using a bike pump to pressurize the launcher, sometimes the foot/check valve in the bike pump or the hose or chuck will leak.  This leak allows the pressure below the yellow QEV diaphragm (in Figure 2, step #8) to become lower than the pressure above the diaphragm and in the black pipe.  This prevents the QEV from sealing properly.  This is a rare occurrence, but we have added a ball check valve to the kits starting 4/2016
  3. Leaks in the slide valve assembly.  Check for leaks and reseal per process 2. above.
  4. Diaphragm within QEV sticks.  Sometimes, when using a bike pump, the QEV diaphragm  (in Figure 2, step #8) will fail to seal the outlet, and the air will leak out the launch tube with each pump, sometimes making the rocket slowly slide up and off the launch pipe.  There is one super-easy trick that almost always works if the QEV diaphragm fails to seal.  First, with the slide valve in the “Launch” position, complete one stroke on the bike pump.  This will build up pressure in the hose of the bike pump.  Next, slide the valve to the “Pressurize” position.  The sudden inrush of pressure built up in the pump hose will almost always seat the QEV diaphragm.  We have found that the more you launch, the more the diaphragm gets broken in.  Now, pump up the chamber normally. Here’s a video showing the process:

  5. QEV “honks” like in the video above, and the pressurized line trick demonstrated in the video doesn’t get it working.  Sometimes, there can be debris that settles on the top sealing face of the QEV diaphragm. We have had a couple instances of some strings of teflon tape that have come loose and started to blow out of the system with each launch. The QEV is threaded together, and can be disassembled to check the diaphragm surface.  Even though the QEV is new, it can still have a bit of debris in it from the factory causing it to not operate correctly.  The QEV can be taken apart without removing it from the wood stand by following the directions below.

If needed you can take the QEV apart carefully and make sure it’s super clean inside.  See pictures below for details:

1. So, you don’t need a vise to open the QEV.  as you already have the launcher fully assembled, you can use the black pipe as a wrench when you unscrew the QEV.  Angle the launch tube horizontal, so when you are loosening the cap, you are pushing downward toward the floor, like this using an adjustable wrench: Assembly Photo

2. Or like this with pliers: Launcher Assembly Photo

3. Once the cap is loose, it is usually easiest to unscrew it completely when the the orange tube disconnected.  To disconnect the tube, push inward on the blue ring, which releases the teeth gripping the tube, then you can pull out on the orange tube.  Once you have the cap removed, it looks like this: Launcher Assembly Photo

4. You can now remove the diaphragm from the body of the valve and inspect the seat.  It should look like this: Launcher Assembly Photo

Check for anything across the surface of this inner gray circle.

5. I usually put the diaphragm in the removed cap, as it is somewhat greasy with petroleum jelly.  Check the top flat face for debris, which may get stuck in the grease.  This one is clean: Launcher rubber valve Photo

6. Reinstall the diaphragm in the body of the valve in the orientation shown below: Launcher rubber valve Photo

7. Next, check the seal between the QEV cap and the valve body.  It’s a clear silicone ring, which can be difficult to see in the grease.  It looks like this: Launcher rubber valve Photo

8. Now thread the cap back on to the body by hand.  Loosen the wingnut and flip the launch tube to the opposite side of the launcher, and tighten the wing nut.  Now you can tighten the cap while again pushing downward toward the floor.  You can again use an adjustable wrench like this: Launcher wrench assemble

Or you can use pliers like this: Launcher adjustable wrench assemble
It takes longer to explain this than it really is to do it.
If this does not work, or if you have difficulty, just let us know and we’ll get you a replacement valve ASAP or send you a replacement kit.  We would just ask that you send us the first kit back so we can inspect it and find the root cause of the problem so we can learn from this.

It’s super simple to connect your Air Rocket Launcher directly to an air compressor.  Instead of attaching the Schrader valve/Check Valve to the “Launch” side of the slide valve, screw in a 1/4″ NPT Male Quick Connect Compressor Fitting.  Set your compressor output pressure to about 100 psi.   Slide valve back towards the compressor to launch and then forward towards the launcher recharge.  Launcher will be ready immediately for the next launch.



  1. We want to be in as many science museum shops as possible.  Do you know someone that works in a museum?  Share our website with them, show them  your rocket and tag them in videos of your rocket you share on social media.
  2. Invite friends to see the launch of your rocket, loan your launcher to your local school or better yet, help a teacher do a launch day with their class.
  3. Share your launches on Facebook, Instagram, Youtube, Twitter and Reddit.  Tag us in the shares!
  4. Like and share our pages on as many social media venues as possible!
  5. Help by volunteering at a local Maker Faire using one of our kits, or help us at one of the larger faires that we attend.  In most cases, you will get free admittance if you volunteer for a few hours.  Contact us if you are interested by going to the upper right menu, hoover on “About Us” the drag your cursor down to “Contact Us.”