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topic 59299

Pump Fittings Clamp Load Differences due to Hexavalent vs Trivalent Coating?

June 18, 2013

Q. Hi. We manufacture loaders for sale. The drive motors (pump side) use mfg fittings that are finished in trivalent and hexavalent chrome. Some brands we use include Piper Brand product which, in use have the appearance to be a hexavalent topcoat, while the Parker Brand and Samson Brand appear to have a trivalent topcoat. The clamp loads and set torques when hoses are tightened to these fittings varies quite a bit @ 98 ft-lbs torque. We are striving to understand why the clamp loads should vary. Some fit-ups see the drive motor hoses self-loosening under loader use and therefore hydraulic leaks occur. Any ideas how the coat differences effect torque and clamp load? Thank you in advance.

Andrew Mills
Quality Control Dept - Gwinner, North Dakota, USA

June 19, 2013

A. Hi Andrew,

In my opinion, you should look in the topcoat specs in both suppliers. Topcoat usually have a integral lubricant that stabilizes (or not) the friction coefficient in some value. The lower this number, the more you will get in clamp load for the same torque, and vice versa.

There are some machines that measure this friction coefficient, but normally there is a clamp load for some torque, and this two values are informed to the supplier and they should look for the correct topcoat that achieves the condition you must get.

I hope this helps! Regards,

Daniel Montanes
- Cañuelas, Buenos Aires, Argentina

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