Starting Conditions of a Centrifugal Pump
Starting Conditions of a Centrifugal Pump
(OP)
As I know two way are used for starting a Cen. pump:
Closed Delivery Valve
Open Delivery Valve
In an oil and gas plant, the starting condition is chosen by instrument&control discipline or process discipline?
The problem is we have high NPSHr (exceeding NPSHa) at the end of curve and if the pump starts with open delivery valve the pump will have NPSH problem in any starting time.
In our data sheet it is written "Automatic Start With Open Delivery Valve".
Can I change starting condition as a mechanical engineer?
Thank you all!
Closed Delivery Valve
Open Delivery Valve
In an oil and gas plant, the starting condition is chosen by instrument&control discipline or process discipline?
The problem is we have high NPSHr (exceeding NPSHa) at the end of curve and if the pump starts with open delivery valve the pump will have NPSH problem in any starting time.
In our data sheet it is written "Automatic Start With Open Delivery Valve".
Can I change starting condition as a mechanical engineer?
Thank you all!





RE: Starting Conditions of a Centrifugal Pump
Why can't you start with a throttled condition? Or install a startup line that runs back to the pump if there are concerns with starting with the valve wide open?
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RE: Starting Conditions of a Centrifugal Pump
Just because the application data sheet gives you X NPSHa and the pump data gives you Y NPSHa doesn't necessarily mean a problem.
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: Starting Conditions of a Centrifugal Pump
On the other hand, if there is not a second pump and if there is not a check valve with full process pressure on the other side, then you will have more difficulty. If it needs to start automatically, then you won't be able to ask an operator to throttle the discharge for start-up. For most pumps, running off the right side of the curve even with inadequate NPSH does not cause significant damage. For a vertical turbine pump with many stages, it can be disastrous. You would need to provide more information about your particular pump for us to evaluate the risk properly.
For our tank transfer pumps, we would be worried about starting up with an open discharge because of the possibility of water hammer in the line. We would install a motor operated valve or control valve that would default to the closed position (or partially open position) and then open fully at a designed rate once the pump has been running for some period of time. The particular settings would be tuned to the particular application, system design, pump design, etc.
Johnny Pellin
RE: Starting Conditions of a Centrifugal Pump
RE: Starting Conditions of a Centrifugal Pump
As started above, a proper study of startup and shutdown operating condition needs to be done with input and exchange of ideas and issues between all disciplines. This is often left to the HAZOP before it is really studied, but you should raise your concerns and issues with the process and controls engineers to see what needs to be done in your particular instance.
In reality pumps often survive startup which is outside their normal operating range, but good design should avoid this as sometimes the pumps don't start if you let them go off the curve on startup and then various mods need to be made by the commissioning and operations teams.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Starting Conditions of a Centrifugal Pump
Independent events are seldomly independent.