Yamada 771261 Diaphragm, Viton for NDP-25
The Yamada 771261 is the genuine Viton (FKM) diaphragm for NDP-25 Series pumps including NDP-25BAV and NDP-25BSV. It is the part that actually moves the fluid: compressed air pushes one diaphragm out while the center rod pulls the other in, so one chamber discharges while the other fills, and the pump alternates between them for as long as air is supplied.
Failures come from flexing, from chemical attack, or from being run dry against a closed valve. Flex fatigue shows as cracking in the convolution where the material bends; chemical attack shows as swelling, softening or a chalky surface; heat shows as hardening and loss of flexibility. Whatever the cause, the fix is the same, and it is worth working out which one it was, because the answer decides whether the replacement should be the same material.
Key Features
- Genuine Yamada replacement diaphragm
- Material: Viton (FKM)
- Fits NDP-25 Series pumps including NDP-25BAV and NDP-25BSV
- Two per pump - always replace diaphragms in pairs
- Restores full stroke volume and flow
- Molded to the factory profile for correct flex life
Applications
- NDP-25 Series pumps including NDP-25BAV and NDP-25BSV
- Scheduled diaphragm changes on transfer and dosing duty
- Restoring lost flow and slow cycling
- Repairing a pump venting product from the muffler
- Converting a pump to a different elastomer for a fluid change
- Marine, industrial, chemical and washdown service
Specifications
- Brand: Yamada
- Manufacturer: Yamada America
- Manufacturer Part Number: 771261
- Part Type: Diaphragm
- Material: Viton (FKM)
- Fits: NDP-25 Series pumps including NDP-25BAV and NDP-25BSV
- Quantity Used: Two per pump
- Series Port Size: 1 in on the NDP-25 Series
- Condition: New
Frequently Asked Questions
Q: Why replace both diaphragms when only one failed?
The second one has seen exactly the same number of cycles and the same fluid, so it is close behind. Beyond that, two diaphragms of different age and stiffness load the center rod unevenly and shorten the life of the new one.
Q: Product is coming out of the muffler. What does that mean?
That is the signature of a split diaphragm. The fluid side has broken through into the air side and is being vented through the exhaust. Stop the pump, because the air motor is now getting product through it and the valve internals will suffer.
Q: Which diaphragm material should I choose?
It depends on the fluid, the temperature and how abrasive the product is. PTFE handles the widest chemical range but flexes less freely, Santoprene and Hytrel give long flex life, Buna-N suits oils and fuels, EPDM suits water and many chemicals, and Viton suits aggressive service.
Q: How tight should the diaphragm plates be?
Tight enough to seal, following the factory torque figures and tightening opposite bolts in sequence rather than working around the circle. Overtightening pinches the bead and starts a crack at exactly the point that flexes most.
Not sure this is the right part? Send us a Picture of the Pump Plate on your pump and the CLR Marine team will confirm the correct diaphragm.
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