January 29, 2020 | 5 minute read
Mechanical split seals are designed for relatively low-duty pumps used in many industries for aqueous applications where the process fluid being sealed would not be considered hazardous. The biggest advantage of split seals is that the pump motor does not need to be completely disassembled to get to the seal, reducing installation and maintenance time and labor.
Split seals, newly shipped from the factory, are preassembled into three different sub-assemblies:
- Rotator assembly with a mating ring, which attaches to the shaft
- Primary ring assembly
- Gland-plate assembly
Although supplied installation and assembly procedures are very complete, it doesn't hurt to punch up a couple points.
Below are seven tips to ensure your split seal installation goes smoothly:
1. Pre-Assembly Shaft Inspection
Make sure the shaft is free and clear of any debris, burrs, metal from the previous seal installation, and any defects to the shaft, especially in the area where the O-ring seals against the shaft. Shaft nicks should be smoothed out to bring it back to the best condition possible. Measure shaft runout to ensure it is within the tolerance of the seal. If the equipment isn’t within its operating specs, the seal is not going to perform as designed.
2. Inspect the Rotor Assembly of the New Split Seal
Check the new split seal to ensure there are no burrs or chips on any of the mating ring half faces that may have become damaged during shipping. Check to make sure there is a consistent gap between the OD of the mating-ring face and the ID of the mating-ring adapter piece. During shipping, the mating ring may become dislodged from the sealing strip that is located behind the mating ring. If there is a gap, apply pressure with your thumbs up and into the gap and the mating ring will pop back into proper position. Avoiding this fix will create excessive seal leaking.
3. Setting the Operating Height of the Seal
To set the proper operating height of the seal, the rotor assembly comes with little plastic spacers. Place them on the back side of the mating-ring adapter of the rotor assembly. Lightly press the spacers up against the seal chamber face. If you push too hard, the spacers will bend and affect the proper setting height of the rotor assembly. Tighten the screws and remove the spacers.
4. Go Easy on O-Ring Lubricant
Sometimes installers in the field get too liberal with O-ring lube on the elastomers; you only need very little O-ring lubricant to do the assembly. The lubricant is only there for ease of assembly, not to help the seal to operate. If too much lubricant is used it can migrate to hot spots where the split faces make contact, resulting in blistering, chipping, seal damage and leakage.
5. Check the Position of the Rotor Assembly on the Shaft
Once the rotor assembly is put together on the shaft, where the split-joint comes together, drag your fingernail across the split, ensuring that the joint is a smooth surface. Your fingernail should not snag on anything. If any raised edge catches, the parts have not gone together correctly, and the seal should be disassembled and inspected to find out why the seal faces are not fitting tightly together.
6. Primary Ring Installation
Whether it is a carbon or silicon carbide primary ring, which is split into two halves, the retaining ring is used to hold the halves together while you do the assembly. Lay the primary ring on the face of the rotor assembly, center it and turn it to make sure everything is smooth. If it doesn’t mesh right, it is not going to operate properly.
7. Gland Plate Installation, and Final Split-Seal Assembly
Installation of the two gland plate halves will complete the split-seal assembly. Put the bottom half of the gland plate under the primary ring so it engages and center the plate over the shaft using a different set of little plastic spacers. Bring in the upper gland plate, align the captive screws with the holes in the lower plate and tighten. Be sure to remove the plastic spacers. Finally, evenly torque the three assemblies together, flush up against the seal chamber face of the pump, with no gaps.
Watch a short video about John Crane’s 3740XL split seal that extends operational life to equipment and reduces maintenance cost due to reduction of seal leakage.
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