Measure seal cxhamber pressure on test bed - why?
Measure seal cxhamber pressure on test bed - why?
(OP)
I have taken over a job that is over half way through and the company has ordered a raft of API610 centrifugal pumps of various sizes for an upgrade project from one vendor. As an additional requirement to API610, the company has asked for the seal chamber pressure to be meaured and recorded on test (mostly tandem seals used). Nobody at the company or the pump supplier can give a solid reason why this should definately be carried out and why it has been asked for. For some of the pumps, the vendor states there is no practical way to do this on test. What do the experts think please? Should I waive the requirement where the vendor thinks it is too difficult to do? The pumps range in size from small up to about 750kW and various discharge pressures upto about 60 bar. Thank you.





RE: Measure seal cxhamber pressure on test bed - why?
Johnny Pellin
RE: Measure seal cxhamber pressure on test bed - why?
I'm gonna add a +1 to JJ's statement. In my world, we pump light hydrocarbons (ethane, propane, butane) which have high vapor pressures. The risk of having product flashing at the seal faces is a serious one, since having a liquid seal running on a film of gas is not an optimal condition.
I have done some testing of seal chamber pressures by putting gauges on the stuffing box ports off the balance line (BB3 pump). It's not perfectly accurate, but it gives me a reasonable guess to say if I'm getting a low vapor pressure margin.
There are several "rules of thumb" for the seal chamber pressure, but they are based on some broad assumptions about the pump and the configuration of the flush, balance lines, and bushing clearances. I've seen some fairly large imbalances between seal chambers on multi-stage BB3 style pumps due to that.
RE: Measure seal cxhamber pressure on test bed - why?
RE: Measure seal cxhamber pressure on test bed - why?
This is combined with the changing dynamic loads since the pump is VFD driven and sees a variety (C2s all the way to C5+) of product densities.
We have yet to have a "seal failure" in the sense that product was allowed to pass the primary seal, and the few seals we have replaced were usually in a near-perfect condition.
RE: Measure seal cxhamber pressure on test bed - why?
RE: Measure seal cxhamber pressure on test bed - why?
RE: Measure seal cxhamber pressure on test bed - why?
Flexibox is correct on all his points. Proper pre-charge on your accumulators, good thermal expansion allowance (our barrier pressures can range about 150 psig during a daily thermal cycle), and a way to vent the system are all necessary.
If you can get a good set of simple instructions (are these systems automated refill?) for the operations folks to follow, these type of seals work very well in harsh conditions.
RE: Measure seal cxhamber pressure on test bed - why?
Did you know that 76.4% of all statistics are made up...
RE: Measure seal cxhamber pressure on test bed - why?