Cute!
I am talking about pumps!
Can you explain what dead head is?
I have to size a pump for 465 gpgm @ 200 psi. If I look at the pump curve I can choose the right pump model and size but always need to keep in mind dead head. Can you explain dead head?
Thanks,
Paula
Very briefly, pump dead head/shutoff head is where all power is delivered to no net flow out of the pump, so all power is being input only to the fluid contained within the pump itself. The high pressure fluid spills back past the impeller clearance into the intake area again. Look at the pump's efficiency at zero flow and you see it is very low, signifying that almost all the energy spent is being converted into heating up that little bit of trapped fluid. It will usually overheat quite rapidly, build up temperature and boil the fluid, dry seals and bearings.... and pretty soon you're smoked. Continued operation below 20% of BEP flow will usually start heating up the fluid, below 10% you will usually get some pretty fast temperature buildups to damaging levels. So startup flows should start at a minimum of 20% of pump BEP and build up as fast as possible to say around 40% and then continue up to 60% minimum as per the suggested operating range for API pumps you can see on thread, thread407-186675: Operating region for pumps according to API
Dead head is the head produced by a pump at zero flow. You don't want to size your pump such that the system curve intersects the pump curve "near" the pump's dead head value. Otherwise, the pump will deliver no flow (which is usually the point of utilizing a pump) and the pump will fail prematurely. There are many definitions for "near". I just try to keep it away from the horizontally flat portion of the pump curve. If you size a pump in this region, small changes in the system curve will result in large changes in flow. It was also shorten the life of a pump.
Try to select a pump curve that intersects the system curve close to the best efficiency point, aka BEP. This is the simple answer to your question.
Some pumps have lower head at zero flow than at some small flow. As you pinc the discharge valve the flow rate will drop, then as you close some more, bing zero flow and a .1% change in valve position, bing it flow at some rate. In this case, the pump is in surge.
![[orientalbow]](/data/assets/smilies/orientalbow.gif "[orientalbow] [orientalbow]")
