Yamada 771256 Diaphragm, EPDM for NDP-20
The Yamada 771256 is a factory EPDM diaphragm for NDP-20 Series pumps including NDP-20BSE and NDP-20BAE. It separates the air side of the pump from the wet side, and it is the only moving part in direct contact with both, which is why it is the component that sets the service life of the whole pump.
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: EPDM
- Fits NDP-20 Series pumps including NDP-20BSE and NDP-20BAE
- 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-20 Series pumps including NDP-20BSE and NDP-20BAE
- 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: 771256
- Part Type: Diaphragm
- Material: EPDM
- Fits: NDP-20 Series pumps including NDP-20BSE and NDP-20BAE
- Quantity Used: Two per pump
- Series Port Size: 3/4 in on the NDP-20 Series
- Condition: New
Frequently Asked Questions
Q: What shortens diaphragm life most?
Running against a closed discharge, air pressure above the pump rating, and cavitation from a starved suction line. All three make the diaphragm work harder than it was designed to on every stroke.
Q: Do I need to change the center disks at the same time?
Inspect them. The disks clamp the diaphragm and any burr, dishing or corrosion on them is transferred straight into the new diaphragm as a stress point, so a marked disk is worth replacing while the pump is open.
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.
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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