Yamada 640043 O-Ring 44.7 mm x 3.5 mm, Buna-N for NDP-20 and NDP-25
The Yamada 640043 is the factory o-ring specified for NDP-20 and NDP-25 Series pumps. It seals one of the joints inside the pump, and because it costs almost nothing next to the downtime a leak causes, it is the kind of part worth replacing on sight rather than on schedule.
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: 44.7 mm x 3.5 mm
- Fits NDP-20 and NDP-25 Series pumps
- Two per pump in the assemblies that use it
- Restores a positive seal at the joint without machining or adjustment
Applications
- NDP-20 and NDP-25 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: 640043
- Part Type: O-Ring
- Material: Buna-N (NBR), 70 durometer
- Nominal Size: 44.7 mm x 3.5 mm
- Fits: NDP-20 and NDP-25 Series pumps
- Quantity Used: Two per pump
- Series Port Size: 1 in on the NDP-25 Series
- Condition: New
Frequently Asked Questions
Q: Is a sleeve O-ring different from a body O-ring?
Functionally it is the same static seal, but the ones on the air valve sleeve see constant reversing pressure and a lot of cycles, so they are usually the first to go and are worth replacing whenever the air valve is stripped.
Q: Can I reuse the old O-ring if it looks fine?
It is a false economy. A ring that has been compressed for months has taken a set in the shape of its groove and no longer springs back against the sealing faces. It will often pass a dry test and then weep once the pump is running under pressure.
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.
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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