Minimum Flow Issues, Seals Failing Quickly...
Minimum Flow Issues, Seals Failing Quickly...
(OP)
About 6 months ago our client installed a Sulzer APT 53-6(O), a pump I selected, and we have been receiving reports from the field that they are having issues with it. It operates 3 gasoline truck loading arms. The problem is when one arm is operating the pump sounds like a concrete truck mixing...
We have heard that when 2 or 3 arms come on that the loud noises subside; based on that fact, an NPSH issue for this pump was ruled out because a higher flow would make NPSH issue worse, not make it go away.
The pump seems to be suffering from MCSF issues. I understand that with one gasoline loading arm on (600 gpm) it is operating outside the preferred operating region (see attached pump curve) which can shorten seal life but they have been through 3 seals since the pump became operational 6 months ago. The pump operates on a VFD and there is a control valve downstream programmed by an Accuload.
Anyone have any suggestions as to why this is happening?
We have heard that when 2 or 3 arms come on that the loud noises subside; based on that fact, an NPSH issue for this pump was ruled out because a higher flow would make NPSH issue worse, not make it go away.
The pump seems to be suffering from MCSF issues. I understand that with one gasoline loading arm on (600 gpm) it is operating outside the preferred operating region (see attached pump curve) which can shorten seal life but they have been through 3 seals since the pump became operational 6 months ago. The pump operates on a VFD and there is a control valve downstream programmed by an Accuload.
Anyone have any suggestions as to why this is happening?





RE: Minimum Flow Issues, Seals Failing Quickly...
You could also be aggravating NPSH(available) issues if the over-recirculation causes overheating of your fluid, probably unlikely though considering that your system is fine at a much higher flow.
Why did your vendor specify this pump for you if 1 arm/600 gpm was an operational case?
RE: Minimum Flow Issues, Seals Failing Quickly...
Johnny Pellin
RE: Minimum Flow Issues, Seals Failing Quickly...
It has basically the minimum amount of straight run pipe; five pipe diameters before there is a 90° bend. Attached is a few screenshots of the piping layout. Can you elaborate on, "This can be very difficult to suppress with excess NPSH margin?"
RE: Minimum Flow Issues, Seals Failing Quickly...
Johnny Pellin
RE: Minimum Flow Issues, Seals Failing Quickly...
Agreed, it does sound like this pump is operating at below MCSF of 400gpm or so when only one loading arm is in operation,since you've ruled out NPSH issues here.
Either reset the control valve at the loading bay to keep this pump above 400gpm during startup, or install a min flow recyle line with return to source tanks.
The flow transmitters at the loading bays should tell you if the min flow of 400gpm is exceeded at startup??
The short life on the shaft seals may or may not be related to this MCSF problem, given that these seals are in volatile gasoline service.
RE: Minimum Flow Issues, Seals Failing Quickly...
600 gpm is not outside the operating range at reduced speed. I would suggest the blue envelope is the operating range at the higher speed.
What is the pump running speed at the 3 flow conditions?
How is speed controlled for the 3 different operations?
Are the operators reducing speed for the lesser number of loading arms or are you assuming they do?
Can see no good reason for failures if the unit is installed correctly and operating at the speed selected for each condition.
Without knowing all facts I would say the pump is not seeing any speed reduction during operation.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Minimum Flow Issues, Seals Failing Quickly...
might be something like this
I'm also puzzled by the following:
What is the pump VFD controlling to - flow? pressure?, fixed speed?
What is the control valve controlling to? flow? fixed pressure?
The flow friction seems to be quite high??
Do you have confirmed operating data ( flow rates, temperature, pressures etc?) How does the arm and pump operate? Often flow is reduced at the start and end to avoid splashing and overfill. If the pump also comes on and stays on for a while at the beginning and end this won't be good.
Basically though it seems you have specified a pump which cannot really do the 3:1 turndown as it is just a bit too big and the turndown is hard to achieve.
So either vary how it works, add a re-circulation line to up the minimum flow when only one arm is loading / shut in head.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Minimum Flow Issues, Seals Failing Quickly...
Would say there is absolutely nothing wrong with the pumps, with the selection, and is not an NPSHa/r problem, the problem is in the operation and the way the pumps are being forced to operate. Are they running at reduced speed for reduced flows, are they running against a closed valve during change-over of the trucks (more than likely YES)
It's the old never ending always touted story - "there is something wrong with the pump" wish I had a $100 for every time I have heard that utterance when in fact the pump was innocent of the charge - I could now be living like a king in my retirement.
CHECK THE OPERATORS, DON'T BELIEVE THEM, CHECK YOURSELF.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)