Startup Bypass Loop
Startup Bypass Loop
(OP)
So, I've been having an incredibly difficult time getting a solid answer on this. I'm a pretty inexperienced EE so pumps are not really my specialty.
I'm a bit confused about the purpose of a start up bypass loop. These are centrifugal pumps that start against a closed discharge valve to prevent run out conditions. However there is also a bypass loop that will begin to close once the discharge valve is fully open.
Can anyone explain what this is achieving? I've never seen this before... someone has mentioned that it helps prevent deadheading, but how can deadheading be prevented if you're still starting the pump against a closed discharge? Does this bypass loop really have that big of an effect on the system curve when the valve starts opening?
I see pictures of bypass loops but they typically have this bypass loop upstream of the discharge valve. So when you start your pump, the discharge valve can be closed and correct sizing of the bypass line should put your pump in safe operating conditions.
Here is what I'm talking about. I've excluded the suction valve but there is one. You can see there is the discharge (closed when starting) and then the bypass valve (open when starting). Once the pump starts, the discharge opens. Once fully open, the bypass valve closes.
http://postimg.org/image/i05izod21/
I'm a bit confused about the purpose of a start up bypass loop. These are centrifugal pumps that start against a closed discharge valve to prevent run out conditions. However there is also a bypass loop that will begin to close once the discharge valve is fully open.
Can anyone explain what this is achieving? I've never seen this before... someone has mentioned that it helps prevent deadheading, but how can deadheading be prevented if you're still starting the pump against a closed discharge? Does this bypass loop really have that big of an effect on the system curve when the valve starts opening?
I see pictures of bypass loops but they typically have this bypass loop upstream of the discharge valve. So when you start your pump, the discharge valve can be closed and correct sizing of the bypass line should put your pump in safe operating conditions.
Here is what I'm talking about. I've excluded the suction valve but there is one. You can see there is the discharge (closed when starting) and then the bypass valve (open when starting). Once the pump starts, the discharge opens. Once fully open, the bypass valve closes.
http://postimg.org/image/i05izod21/





RE: Startup Bypass Loop
I.e., if you block the bypass, you may blow a fuse.
Don't do that. Take a look at the pump operating points by superimposing the different system curves on the pump diagram, and noting the efficiency or power curves' locations also.
Mike Halloran
Pembroke Pines, FL, USA
RE: Startup Bypass Loop
I may be reading your attachment sketch all wrong, but it appears the recirculating loop is branching off the discharge after the discharge valve. If it is installed the way your sketch shows it (the bypass loop) will be nonfunctional.
Of course there is a lot of items missing from the sketch.
How about adding:
- Flow arrows, upstream, downstream and the loop
- The Suction Block Valve
- the discharge Check Valve
- The source of the suction (Tank, Pipeline, other?), Yes it can make a difference
- Line sizes
prognosis: Lead or Lag
RE: Startup Bypass Loop
See the valves in the link.
http://www.oawu.net/Pdf/CV_STM_Section_3_Applicati...
You need to provide further details for someone to understand your exact application.
RE: Startup Bypass Loop
Johnny Pellin
RE: Startup Bypass Loop
RE: Startup Bypass Loop
The best sources for this sort of thing are often identified as having a 'bad attitude'. ... because they care, or cared once upon a time.
It might cost you some beer and pizza, always a good investment.
Mike Halloran
Pembroke Pines, FL, USA
RE: Startup Bypass Loop