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Pet Forum / Aquaria / Marine Reef / June 2005sump pump question
Where do you measure from to get the distance for the head above a sump pump? Do you measure from the pump in the sump to the water level in show tank or do you measure from the top water level in the sump to the water level in the show tank? I'm trying to figure out which pump I need, or is it better to just get an over sized pump and use a ball valve to get the flow to the right rate. Thanks. > Where do you measure from to get the distance for the head above a > sump [quoted text clipped - 7 lines] > get the > flow to the right rate. Thanks. You measure from the pump intake to the highest point the water must travel, generally the portion of pipe that snakes over the rim of the tank. >>Where do you measure from to get the distance for the head above a >>sump [quoted text clipped - 11 lines] > travel, generally the portion of pipe that snakes over the rim of the > tank. Billy, This is not correct it should be measured from the water level in the sump to the water level in the tank, the up over the rim, unless you have a siphon break at the rim will siphon back down into the tank so you do not have to worry about the up and over. Plus in your sump the water level in the sump creates a pressure to feed the pump that is equal to the height of the water above the pump so the head starts at the top of the water in the sump. Kim > This is not correct it should be measured from the water level in > the sump to the water level in the tank, the up over the rim, > unless you Yup, you're right. I did a bit of re-reading, and you're spot on. billy Hi Kim, The pump head is the hight that the pump will raise the water (or any liquid) above the pump inlet, the depth of water in the sump has no measurable effect on the pump head, if the return goes over the top rim of the tank the depth of water in the tank has no bearing on the head ether. All manufacturers quote the flow rate at various head heights which they could not do if it depended on water depth in the sump. regards, unclenorm. > >>Where do you measure from to get the distance for the head above a > >>sump [quoted text clipped - 23 lines] > > Kim I'm sorry but you are incorrect. The presure on the intake of the pump effects the head pressure of the pump. If the return goes over the top rim of the tank it can effect head pressure but only if it has a siphon break at the top if the water is able to siphon back down into the tank then the height above the water does not count. Yes they can quote flow rate at various head heights even if it depended on the intake head pressure. First when they quote flow rates, most of it is done via calculations not measurements. then they get a flow curve for the pump then from the flow curve they list a few interesting points for you to look at. The way a centrifugul pump works is that it adds pressure to the water. If you have a pump that adds 10 psi and you have 5 psi water at the intake of the pump you will get 15 psi of pressure out the output. This wil effect how high the pump will pump as well as how much it will pump at any head pressure. If you have 0 psi at the pump intake that same pump will only put out 10 psi rather than 15 so the flow will drop by around 1/3. Kim > Hi Kim, > The pump head is the hight that the pump will raise the water [quoted text clipped - 34 lines] >> >>Kim Hi Kim, I'm sorry to have to tell you your talking a lot of twaddle, my statement is perfectly correct, do some more research, think if the manufacturer made an untrue statement they would be contravening the trade descriptions laws and would be liable to prosecution. Also if you had say an 8" head at the pump inlet (due to water level in the sump) then you would also have an opposing 8" head in the pump outlet pipe!!. As for a siphon break, it would have no effect on the pump head whatsoever, regards, unclenorm. You can easly test this out also, just get a garbage can and a small submersible pump in it. take a large diameter hose and run it out of the can just to the top and catch the water in a 1 gallon bucket. Time how long it takes to fill the bucket. Then fill the garbage can clear full of water and time it again. You will find that when the garbage can is full the pump will pump out more water, now the only reason that this could happen is that the pump has less head pressure on it (it has to lift the water a to a lower height). Kim > Hi Kim, > The pump head is the hight that the pump will raise the water [quoted text clipped - 34 lines] >> >>Kim As someone who deals with head pressures almost daily I must concur with Unclenorm. Headpressure ratings are how far it will pump above the pump, which in our case is the rim of the tank, or highest point. After that point it is considered freefall, because all the work is done. Dan You can easly test this out also, just get a garbage can and a small submersible pump in it. take a large diameter hose and run it out of the can just to the top and catch the water in a 1 gallon bucket. Time how long it takes to fill the bucket. Then fill the garbage can clear full of water and time it again. You will find that when the garbage can is full the pump will pump out more water, now the only reason that this could happen is that the pump has less head pressure on it (it has to lift the water a to a lower height). Kim > Hi Kim, > The pump head is the hight that the pump will raise the water [quoted text clipped - 38 lines] >> >>Kim > Where do you measure from to get the distance for the head above a sump > pump? Do you measure from the pump in the sump to the water level in show > tank or do you measure from the top water level in the sump to the water > level in the show tank? I'm trying to figure out which pump I need, or is > it better to just get an over sized pump and use a ball valve to get the > flow to the right rate. Thanks. You measure from the water level in the sump to the water level in the tank. Of course then you have to add in the frictional head loss also. I would always suggest going oversized and use a valve to controll the flow since you never know when you might want to add something new to your tank, like a CA reactor feed off of your return pump, or a fuge or surge device etc. Kim I take it then that its not a good idea to have a largish pump and run it flat out, for I was planning such a thing on my 42 Gallon tank. Robin You also have to add in additional head length for elbows, bends and T's.... Each elbow adds enough flow resistance to equal a significant amount of head length. I would have to do a search to find some specifics.... (Anyone here WELL versed in fluid dynamics?) Unless a person is really worried about energy consumption or heat, then just buy one plenty big and use a valve AFTER the pump to control flow rate... >> Where do you measure from to get the distance for the head above a sump >> pump? Do you measure from the pump in the sump to the water level in show [quoted text clipped - 13 lines] > > Kim > You also have to add in additional head length for elbows, bends and T's.... > Each elbow adds enough flow resistance to equal a significant amount of head [quoted text clipped - 6 lines] > just buy one plenty big and use a valve AFTER the pump to control flow > rate... The amount of frictional losses are determined by the velocity of the water in the pipe, so if you increase the size of the pipe even with lots of elbows bends T's etc, there will be very little flow loss. This is why I always say go at least one pipe size larger, and even better 2 pipe sizes larger. You can use the head loss calculater on reefcentral to give you an idea of the head losses you will have. It is not perfect since the type of pipe you use (ie schedule 40/80 or the thin wall) will effect the flow rate quite a bit plus different manufactures have different coeffectiants of friction, but it is a very good aproximation. Kim Question, instead of 90 degree elbows what about long-radius elbows. That should reduce head pressure, Right? Frank > > You also have to add in additional head length for elbows, bends and T's.... > > Each elbow adds enough flow resistance to equal a significant amount of head [quoted text clipped - 18 lines] > > Kim Yes a long radius elbow will reduce the head pressure over a normal elbow, but what will reduce it the most is going to a large diameter pipe. If you increase your pipe from from 1 to 2 sizes larger than you think you need, the friction of elbows and other fittings is pretty close to zero so you do not need to worry about any fittings to put on the pipe even if you have the pipe doing figure 8s. Since with the larger diameter the velocity is lower, it is easier for the water to change directions. Kim > Question, instead of 90 degree elbows what about long-radius elbows. That > should reduce head pressure, Right? > > Frank |
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