Two important aspects of ensuring rotary union functionality are making sure they do not experience high torque and ensuring they do not leak under any conditions.
At United Equipment Accessories (UEA), once the swivel is fully assembled, it is placed into our test stand where it is prefilled with hydraulic fluid and rotated in each direction. While rotating the rotary union, we measure the torque values. If the rotary union’s torque is too high, we then investigate to determine why this is happening. Possible causes could include tolerances being too tight on the swivel housing or the spool, a seal improperly seated in the swivel, or seal grooves out of alignment.
After we ensure that the torque is within the proper range, we check to make sure the rotary union does not leak under any circumstances. We pressurize each circuit to 1.5 times the operating pressure (with a max. of 7,500 psi) checking to see that there is no drop in pressure. This test ensures there are no leaks while the customer is operating the rotary union under their normal operating pressures.
We also test the rotary union at low pressures up to 400 psi to confirm that we do not have a leak when the rotary union is not being operated. The low-pressure test makes sure that the u-cup seals, located at the ends of the rotary union, do not leak.
If we do encounter a leak, we take the rotary union apart to inspect the cause of the leak. This might be due to the seals getting nicked during assembly, the seals improperly seated in the rotary union, or the seal grooves misaligned.
Once the rotary union passes all torque values and pressure tests, the torque and pressure values are recorded and stored for reference for each rotary union to give our customers confidence that our rotary unions will perform in their real-world applications.