Yamada 640036 O-Ring 35.5 mm x 3.55 mm, Buna-N for NDP-20
The Yamada 640036 is a genuine o-ring used in NDP-20 Series pumps. An air operated double diaphragm pump is a stack of machined parts clamped together, and every joint in that stack depends on an elastomer seal like this one sitting correctly in its groove and holding its shape under compression.
Elastomer seals fail in a predictable way. Heat and time take the flexibility out of the rubber, the ring takes a permanent set in the shape of its groove, and it stops pushing back against the surfaces it is meant to seal. Chemical attack does the same job faster, swelling the ring until it will not fit the groove or hardening it until it cracks. Either way the first sign is usually a weep rather than a spray, so it pays to look at the joint faces whenever the pump is apart.
Key Features
- Genuine Yamada replacement o-ring
- Material: Buna-N (NBR), 70 durometer
- Nominal size: 35.5 mm x 3.55 mm
- Fits NDP-20 Series pumps
- 4 per pump in the assemblies that use it
- Restores a positive seal at the joint without machining or adjustment
Applications
- NDP-20 Series pumps
- Scheduled rebuilds and seal kit top-ups
- Chasing a weep at a joint face after reassembly
- Replacing a ring that has taken a compression set
- Service after a fluid change that attacked the old elastomer
- Marine, industrial and transfer duty
Specifications
- Brand: Yamada
- Manufacturer: Yamada America
- Manufacturer Part Number: 640036
- Part Type: O-Ring
- Material: Buna-N (NBR), 70 durometer
- Nominal Size: 35.5 mm x 3.55 mm
- Fits: NDP-20 Series pumps
- Quantity Used: 4 per pump
- Series Port Size: 3/4 in on the NDP-20 Series
- Condition: New
Frequently Asked Questions
Q: How do I stop damaging the new ring during assembly?
Use a plastic or brass pick to remove the old one, clean the groove so no grit is trapped under the new ring, and lubricate it lightly with something compatible with the fluid before closing the joint. Most premature failures are assembly damage, not material failure.
Q: Does the durometer number matter?
Yes. Hardness sets how far the ring deflects under a given squeeze. A softer ring in a groove designed for a harder one extrudes into the gap and nibbles away at the edge; a harder one in a soft ring groove may not fill the groove at all.
Q: Should I replace all the O-rings at once?
If the pump is open, yes. They are inexpensive next to the labor of opening the pump, they have all seen the same hours and the same fluid, and replacing one of a set usually means coming back for the others.
Q: What makes an O-ring swell?
Fluid absorption. The elastomer takes up the liquid it is sealing, grows, and eventually will not fit the groove. A ring noticeably larger than the new one is telling you the material choice is wrong for that service.
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 o-ring.
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