| Larry Bachus
(a.k.a. "The Pump Guy")
Good day Pump Guy,
I am a mechanical engineer in the ash plant at a petroleum refinery. We are experiencing major problems with leaks on the shaft packing of the ash pumps.
When the pumps are re-packed, they run only a short while (sometimes less than 10 minutes) before the packing leaks rather severely. The pressure of the seal water is higher than the pressure on suction of the pump at all times. But, unfortunately there are no pressure gauges installed on the pump like you talked about in your pump course I attended earlier.
The only difference I could discern from my investigation is that the person who has been installing the packing in recent weeks is not the regular pump packer—the regular pump packer retired a few weeks ago.
Can you help with some advice or pointers?
Thanks for writing. Let’s see if I can help. I’ll consider the obvious first.
Is your new pump packer using the correct packing? Packing rings for valves appear similar to packing rings for pumps. However, valve packing is not interchangeable with pump packing.
Some styles of pump packing are made for water pumps. Some styles of packing are made to resist acids. Some styles of packing are made to resist caustics. Some styles of packing are made for slurry pumps, or high-velocity shaft speeds. Be sure the new pump packer is using the correct packing style for the ash pumps.
Assuming the packing style is correct for the application, is your new pump packer trained in the techniques to properly pack a slurry pump?
Packing a pump is an acquired skill like riding a bicycle. Both skills begin with personal desire. A parent (or older sibling or friend) can coach you through finding your balance on the bicycle. An experienced pump packer normally teaches the novice the techniques. The novice must be prepared to fall a few times before dominating the skill.
Packing a cold water pump is like riding a bicycle in your backyard. Packing a big high-speed ash slurry pump is like riding a bicycle through downtown traffic. Is your novice pump packer trained in the techniques to properly pack a slurry pump?
Here are some abbreviated guidelines to pack a water pump:
- Place and seat each packing ring finger tight into the chamber.
- Place the lantern ring so it locates at the flush port hole.
- When all rings are loaded into the chamber, install the gland follower against the rings.
- Tighten the gland nuts onto the gland follower by hand. Do not use wrenches or pliers at this stage to tighten the gland nuts. No more torque than you can muster with your fingers and thumb.
- Open the flush line to the packing.
- Protect the bearings from the leakage or spray.
- Start the pump and go through the break-in procedure.
- Does your new pump packer give the newly installed packing rings a break-in procedure? I’d say that most premature packing failure and sleeve damage results from an inadequate “break-in” procedure.
On starting the pump, permit the pump to leak generously through the packing rings for 10 to 15 minutes. The packing rings will swell as they absorb the flush water similar to the way a dry sponge swells as it absorbs water.
As the rings swell the rings will conform to the shaft (or sleeve) and the bore of the packing chamber. You will notice that the leakage diminishes considerably as the swollen rings fill all voids and leak paths through the packing set.
|Two used sleeves from the same pump that illustrate the importance of the break-in procedure. The sleeve in the foreground is worn evenly and can be used again. The sleeve in the background is destroyed. The packer went for leakage control without going through a break-in period.|
The swollen packing rings will push against the gland follower. Now you won’t be able to further tighten the gland nuts by hand.
Most gland nuts have six sides or flats. With a wrench, tighten each gland nut one flat (1/6th of a revolution). Don’t allow the temperature to rise in the packing. Continue adjusting the gland nuts one flat (1/6th of a revolution) every 10 minutes until the leakage is controlled to about one drop per second per inch of shaft (or sleeve) diameter.
The inexperienced or untrained pump packer tends to go for leakage control at pump start-up, without giving the packing rings time to seat into the stuffing box and adjust to the conditions of the pump.
It is similar to buying new leather shoes, putting-on the shoes for the first time, and then running a marathon in the new shoes. New shoes need a “break-in” period that allows your feet to adjust to their unique contours. If you run a race in new shoes, the shoes will make blisters and sores on your feet.
If the novice pump packer goes for leakage control without a “break-in” period, the heat and abrasion from high-speed shaft rotation will rapidly degrade the packing rings and destroy the pump sleeve, or shaft.
If the packing destroys the pump shaft, you’ll have to replace the shaft. Most packed pumps have sacrificial shaft sleeves that fit onto the shaft. The sleeve is less expensive to purchase than the shaft.
When the pump packing is given a break-in procedure, the sleeve usually wears evenly and can be used a few times. If the pump packer goes for leakage control on start-up, the sleeve may not survive beyond one set of packing.
Installing a new sleeve is relatively easy. Removing a scored sleeve from the shaft can be time and labor intensive. Frequently, the shop mechanic damages other pump parts (the bearings, the shaft) as he removes the old sleeve from the shaft.
If the opportunity arises, send your young pump packer to the Pump Guy Seminar in 2014. For more details, see FlowControlNetwork.com/PumpGuy.
The Pump Guy
Larry Bachus, founder of pump services firm Bachus Company Inc., is a regular contributor to Flow Control magazine. He is a pump consultant, lecturer, and inventor based in Nashville, Tenn. Mr. Bachus is a retired member of ASME and lectures in both English and Spanish. He can be reached at firstname.lastname@example.org.??