Iwaki Pump Disassembly: EHN Pump Head and Diaphragm Step by Step
Iwaki pump disassembly is a seven-stage job: power off, depressurize, flush, remove the pump head, remove the diaphragm, inspect, then reassemble and prime. Get the order right and a full diaphragm change on an EHN solenoid pump is a straightforward bench task. This walkthrough is written for plant technicians, OEM service staff and distributors who maintain Iwaki EHN pumps on water treatment, cooling tower and chemical feed duty.
Know the liquid end before Iwaki pump disassembly starts
The EHN series is offered with several standard liquid end materials: VC and VS (PVC), PC, PS and PP (glass-fibre reinforced polypropylene), plus FC in PVDF and SH in stainless steel. There is also the NAE auto-degassing head for gassing chemicals such as sodium hypochlorite. Standard VC, VS, PC, PS and PP heads carry an air vent valve; on the FC and SH versions, check the data sheet, because availability differs.
Inside, every version has the same basic parts: suction valve, discharge valve, pump head body, O-rings or gaskets, and a PTFE-faced diaphragm. The diaphragm is a PTFE and EPDM laminate. The PTFE side faces the chemical and the EPDM side never touches the liquid, so orientation matters on reassembly.
Take a few phone photos of the head, tubing and valve orientation before you touch anything. It costs ten seconds and prevents most reassembly mistakes after an Iwaki pump disassembly.
Iwaki pump disassembly stage 1: power off, depressurize, flush
Unplug the pump and disconnect any external pulse, analog or STOP signal so a controller cannot restart it mid-job. Open the air vent valve to release discharge line pressure.
If the pump handles hypochlorite, acid or caustic, flush before any Iwaki pump disassembly. Put the suction tube in a bucket of clean water, run the pump for a few minutes until the head and lines contain only water, then stop and isolate again. Opening a head that still holds pressure or chemical is the most common way technicians get hurt. Goggles, chemical-resistant gloves and a drip tray are the minimum.
Stage 2: remove the pump head in an Iwaki pump disassembly
Undo the tubing nuts on suction and discharge, keeping the tube ends pointed away from you. The head is held by screws, typically four. Loosen them in a cross pattern a little at a time rather than fully removing one before the next. That keeps the plastic head from being stressed unevenly.
With the head off, the suction and discharge valve cartridges can come out for cleaning. Ball, seat and housing order is covered in our separate guide to Iwaki EHN pump head and check valve service. The short version: the two valves point in opposite directions, and swapping them gives zero output.
Stage 3: remove the diaphragm during Iwaki pump disassembly
The diaphragm is now visible. On most solenoid pumps it threads onto the drive shaft and unscrews by hand counterclockwise; confirm the method in the manual for your exact model. Do not use pliers. A scratched PTFE face means a new diaphragm.
Some models have a spacer or backing plate behind the diaphragm. Note its position and orientation. Lay every part out in order on a clean cloth as you go, because a missing or doubled spacer changes stroke volume and the pump will under- or over-dose.
Signs the diaphragm should be replaced:
- Scratches, blistering or whitening on the PTFE face
- Chemical staining around the sealing edge
- Any liquid on the drive side, which means it has already leaked through
There is no fixed interval. Chemical, pressure and run hours drive it, and our article on when to replace a metering pump diaphragm explains how to judge it.
Stage 4: inspect and clean
With the parts out, check the pump head cavity for crystals or scoring, and make sure the vent passage is clear. FKM or EPDM valve seats that have hardened or deformed should be replaced rather than reused. O-rings and gaskets are cheap; treat them as single-use.
Clean with water only during Iwaki pump disassembly. Solvents can craze PVC, and a crazed head usually starts weeping within days. Transparent PVC heads have one advantage here: you can watch for trapped air during the test run.
Stage 5: reassemble, tighten evenly, prime and verify
Reverse the Iwaki pump disassembly order. Fit the diaphragm (and spacer, if used) and screw it home by hand. Refit the head and tighten the screws in a cross pattern over two or three passes to the torque in the manual; overtightening cracks plastic heads. Then refit the valves and tubing.
Run on clean water with the air vent open until a steady flow appears, then close it. Check every sealing face for leaks, and measure actual output with a graduated cylinder or calibration column. If the pump clicks but nothing comes out, air is still trapped or a valve is upside down. Our guide to Iwaki EHN not pumping and auto-degassing heads walks through that diagnosis.
Conclusion
Successful Iwaki pump disassembly depends on sequence more than skill. Depressurize and flush first, loosen and tighten head screws in a cross pattern, keep diaphragm parts in order, renew seals every time, then prime, leak test and measure flow on water. For genuine spare parts or a replacement pump, browse our Iwaki brand page and solenoid dosing pumps, then send the nameplate model and chemical and contact our engineers to confirm the right parts.
FAQ
Do I need special tools for Iwaki pump disassembly?
Usually not. A standard hex key or screwdriver removes the head, and the diaphragm unscrews by hand on most models.
The diaphragm will not unscrew. What should I do?
Crystallized chemical is probably holding it. Soak the head area in warm water for a while, then turn it slowly by hand.
Flow dropped after I fitted a new diaphragm. Is that normal?
Not really. Check that no spacer was left out or reversed, then re-prime and confirm valve orientation.
How do I stop leaks after reassembly?
Use new O-rings, tighten head screws evenly in a cross pattern, and leak test on water before reconnecting chemical.
Will opening the pump affect my warranty?
It depends on the supplier's terms. During the warranty period, it is wise to check with your distributor before replacing parts yourself.