REPAIR VIDEO: Diaphragm Replacement on a KAPPA-55

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Step-by-Step Instruction Video for Replacing the Diaphragms

Spray Equipment DIY How To Video

Easily repair the diaphragms on an Udor KAPPA-55 diaphragm pump with these step-by-step instructions and how to video.

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Diaphragm Repair on an Udor KAPPA-55 Pump



  • Ratchet
  • ¾” socket
  • 11/16” socket
  • flat head screwdriver
  • small screwdriver
  • hammer
  • air chuck
  • power drill
  • air gauge
  • brake cleaner
  • Udor 40 WT Non Detergent Oil
  • Udor 8700.26 Diaphragm Repair Kit


  1. Start on the top and remove the head bolts using the 11/16” socket.
  2. Remove the bolt and washer holding the diaphragm onto the piston using the ¾” socket. 
  3. Use the small screwdriver to remove the diaphragm and the piston sleeve.
  4. Drain the pump through the open head into a pan.
  5. Spray brake cleaner to remove any leftover chemical residue.
  6. Repeat the head and diaphragm removal process on the remaining 2 heads.
  7. The first 3 heads are the actual pump heads, housing the check valves and covering the piston diaphragms. The 4th head is the accumulator and houses the accumulator diaphragm. Remove the bolts using the 11/16” socket. Remove the accumulator diaphragm.
  8. Start reassembling the pump. Install the piston sleeve back onto the piston.
  9. Take the piston diaphragm and place it back onto the piston. Make sure the side with more wiring and “water” is facing out towards you when you install the diaphragm.
  10. Put the washer on with the sharp side facing out to prevent it from digging into the diaphragm and tearing it prematurely. Hand tighten and then use the ratchet and ¾” socket to tighten the bolt onto the piston. Ensure the diaphragm is sealed all the way around and reinstall the head onto the pump body.
  11. Poke the check valve to confirm the spring is still opening/closing. The valves will only go in one way and the blocker on the pump body will prevent you from doing it incorrectly.
  12. Start with the pump head with the brackets attached to it. The top two bolts closest to the oil sight glass are the shorter bolts. The two bolts to hold the bracket on and the 5th bolt near the check valves are the longer bolts. Use the power drill with 11/16” socket to tighten the bolts onto to the pump body.
  13. Repeat the steps with the next head.
  14. Lightly hammer the sleeve in and reinstall the diaphragm, bolt & washer and head.
  15. Place head back onto the pump body – checking spring in valves. Note: there are washers on the top shorter bolts, and no washers on the bolts holding the bracket on.
  16. We save the top head for last so we can fill it with oil. Fill the case up to the piston and put the sleeve back in. Tap with the hammer and install the diaphragm with writing facing out. Hand tighten the bolt & washer using the ratchet.  Rotate the crankshaft to seat diaphragm and put top head back on.  For the top head they are all the same length and have a washer. The pump tag & decal will act as a washer for that bolt. Use the power drill and 11/16” socket.
  17. Remove the sight glass lid and top it off with oil. Fill it to halfway up the glass so you can see the consistency.
  18. While waiting for the oil to settle replace the air accumulator diaphragm.  Put it in a bowl – inward to pump body. Put the head on with the air valve accessible.
  19. Use the power drill and 11/16” socket to secure head.
  20. Add some air to the valve – the rule of thumb is 20 psi minimum or 20% of normal operating pressure. Use the air gauge to check the pressure once filling. If you have too much or too little psi in the dome, your discharge lines will pulsate and jump around.
  21. Check the oil sight glass – you will see it bubbled down some – and add more oil if needed.

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