Robbins & Myers 320-3759-000 316 Stainless Nitrile Flexible Joint for Moyno 500 Models 331 to 344
The 320-3759-000 is the flexible joint in 316 stainless steel with NBR nitrile boot for the Moyno 500 Models 331, 332, 333 and 344. It sits between the drive shaft and the rotor and exists to solve a problem that is built into every progressing cavity pump: the rotor does not turn on a fixed centreline but orbits as it rotates, so the connection to the drive has to transmit full torque while allowing that eccentric motion.
The boot is the part that usually fails first. Once it splits, pumped liquid washes out the lubricant and carries grit into the working surfaces, and from there the joint has a short remaining life. Because the joint is buried behind the stator, it is worth replacing on any major rebuild rather than putting the pump back together around a doubtful one. Always check the rotor pin holes and shaft connection for elongation while the joint is out.
Key Features
- Genuine Robbins & Myers Moyno replacement flexible joint
- 316 stainless steel with NBR nitrile boot construction
- Sized for the Moyno 500 Models 331, 332, 333 and 344 drive train
- Transmits full pump torque while absorbing the eccentric rotor motion
- Removes the play that causes knocking and uneven stator wear
- Direct replacement, no modification required
Applications
- Moyno 500 Models 331, 332, 333 and 344 progressing cavity pumps
- Replacing a joint with a split boot or visible free play
- Curing a knock or clatter at the pump end of the drive
- Routine renewal during a stator and rotor rebuild
- Restoring drive to a pump that turns but produces no flow
- Industrial, marine and dockside pumping installations
Specifications
- Brand: Robbins & Myers
- Manufacturer: Robbins & Myers (Moyno)
- Manufacturer Part Number: 320-3759-000
- Part Type: Flexible joint, rotor to drive shaft
- Material: 316 stainless steel with NBR nitrile boot
- Quantity Used: One per pump
- Fits: Moyno 500 Models 331, 332, 333 and 344
- Condition: New
Frequently Asked Questions
Q: The pump turns but nothing comes out. Could the joint be the cause?
It is one of the first things to check. A joint that has failed completely leaves the shaft turning while the rotor stays still or wanders, so the pump sounds normal and delivers nothing. Turn the shaft slowly by hand and watch whether the rotor follows it.
Q: Does the joint need packing with grease on assembly?
Follow the service instructions for your pump build. Some joint designs are supplied ready to fit and others expect a specific lubricant behind the boot, and using the wrong one can attack the elastomer. Send a picture of the pump plate if you are unsure which applies.
Q: Can a joint be rebuilt rather than replaced?
Pins and boots are sometimes available separately, but once the working surfaces inside the joint are worn the geometry cannot be restored, and a rebuilt joint that still has play will keep wearing the stator unevenly.
Q: Why does a split boot matter if the joint still drives?
Because the boot is what keeps lubricant in and the pumped liquid out. Once it splits, grit reaches the working surfaces and the joint moves from gradual wear to rapid failure, usually within a small fraction of its normal life.
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 flexible joint before you order.
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