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Boiler feed pump 1
- Thread starter joken
- Start date
Since pablo02 tried to help me with my 'dirty water' problem I'll jump into the fray, although like your vendors my opinion is the opposite - I prefer packing- its inexpensive, easily changed, and the whole pump doesn't have to be removed to change it- I know a lot of people I work with prefer mechanical seals, but they have to be handled properly, are expensive ( although they can be exchanged or rebuilt), installation more complicated & skill level required much higher
just my 2 censt worth
just my 2 censt worth
joken, Mechanical seals and packings have their advantages and disadvantages in relation to application. They are wearing parts and will always require replacement at some time or another. To get around this problem (and increase MTBF)take a look at mag-drive pumps. No shaft seals here.
Hope this helps.
saxon
Hope this helps.
saxon
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1
- #5
There are a good number of things to consider when choosing between mechanical seals and packing. I generally think that this is one application that is better off with seals. Here is why-
Boiler Feed Water is treated water. Think of the many gallons or liters of water in your system. Then think of all the costs incurred with each unit of volume.
How many drops a minute will your packing leak? Lets say 7.
8760 hrs/yr x 60 min/hr x 5 drops/min x 1 gal/75,700 drops =
48.6 gallons a year. How much does it cost to treat and procure a gallon of water?
How about packing inspection time? Your operators will have to drop by the pump every so often to tighten or inspect the packing. Lets say 28 times a week for 3 minutes each. Enter the average operator labor rate.
28 of checks/week x 0.05 inspection time per pump/hr x 52 weeks x hourly wage rate
How about the power savings? Packing costs an additional 1.5 to 4.5 KW per pump. (more friction to overcome, static and kinetic)
And remember, since packing leaks more than seals do, think of the reduced bearing life. That would be 2 sets of bearings for most Boiler Feed Water pumps.
You'll have to replace your shaft sleeves, possibly even the entire shaft if the packing is tightened down too much for too long.
It starts to add up pretty quickly. Because mechanical seals are repairable, the cost of ownership drops quickly, most times the seal hardware is in good condition, possibly even the seal faces may be in good enough condition to re-lap and return to service.
Taking a little time to choose the proper pump, seal, and seal support equipment makes a big difference in the life cycle cost of the pump.
For Boiler Feed service, think about what the water is treated with. Consider hard faces if there are a lot of minerals, or ferrous materials used. Use a large bore seal chamber and a solid shaft. This makes a huge difference. With a large bore seal chamber you are sure to get the flow you need in the seal chamber to help your seal last longer.
Also, with a large bore you can use a cartridge seal. This makes the argument about the complications of installation disappear. It isn't much more work than to remove the packing follower.
See one of the recent posts (as of this date) in the mechanical seal forum on boiler feed water applications.
And as for mag-drives- How many times have you heard about the repair costs of mag-drive pumps? Think about the cost of repair for a seal and bearing replacement compared to that of replacing the silicon carbide bearings and a set of magnets. Boiler Feed Water is not the easiest service, think about water flashing to steam and how easily the suction side of many multi-stage BFW pumps cavitate.
I think the best bet is to talk to your pump vendor and then talk to a local packing/seal vendor and run your ideas past both of them. If you trust their opinions and choose the best options they have for the money you have, you’re better off.
Boiler Feed Water is treated water. Think of the many gallons or liters of water in your system. Then think of all the costs incurred with each unit of volume.
How many drops a minute will your packing leak? Lets say 7.
8760 hrs/yr x 60 min/hr x 5 drops/min x 1 gal/75,700 drops =
48.6 gallons a year. How much does it cost to treat and procure a gallon of water?
How about packing inspection time? Your operators will have to drop by the pump every so often to tighten or inspect the packing. Lets say 28 times a week for 3 minutes each. Enter the average operator labor rate.
28 of checks/week x 0.05 inspection time per pump/hr x 52 weeks x hourly wage rate
How about the power savings? Packing costs an additional 1.5 to 4.5 KW per pump. (more friction to overcome, static and kinetic)
And remember, since packing leaks more than seals do, think of the reduced bearing life. That would be 2 sets of bearings for most Boiler Feed Water pumps.
You'll have to replace your shaft sleeves, possibly even the entire shaft if the packing is tightened down too much for too long.
It starts to add up pretty quickly. Because mechanical seals are repairable, the cost of ownership drops quickly, most times the seal hardware is in good condition, possibly even the seal faces may be in good enough condition to re-lap and return to service.
Taking a little time to choose the proper pump, seal, and seal support equipment makes a big difference in the life cycle cost of the pump.
For Boiler Feed service, think about what the water is treated with. Consider hard faces if there are a lot of minerals, or ferrous materials used. Use a large bore seal chamber and a solid shaft. This makes a huge difference. With a large bore seal chamber you are sure to get the flow you need in the seal chamber to help your seal last longer.
Also, with a large bore you can use a cartridge seal. This makes the argument about the complications of installation disappear. It isn't much more work than to remove the packing follower.
See one of the recent posts (as of this date) in the mechanical seal forum on boiler feed water applications.
And as for mag-drives- How many times have you heard about the repair costs of mag-drive pumps? Think about the cost of repair for a seal and bearing replacement compared to that of replacing the silicon carbide bearings and a set of magnets. Boiler Feed Water is not the easiest service, think about water flashing to steam and how easily the suction side of many multi-stage BFW pumps cavitate.
I think the best bet is to talk to your pump vendor and then talk to a local packing/seal vendor and run your ideas past both of them. If you trust their opinions and choose the best options they have for the money you have, you’re better off.
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