Why does my plumbing cause pumps to run hot?

[mikester]

I have been fighting this problem for months, but it is obvious to me that my closed loop plumbing is causing whatever pump I add to it to run hot and add 2-3 degrees to the water temperature. I have tried 3 different pumps - an Ampmaster 3000, PanWorld PS150, and Blueline 1100 - all of which are not known to run hot. Also, I have ran the Panworld and Blueline pumps on my return, and they run very cool and add no heat to the water - but when I move either of them to the closed loop, they run extremely hot to the touch and add a lot of heat to the water. So, it's not an issue with the pumps, so the only thing I can think of is that something in the plumbing is making the pump work extra hard and is adding heat.

My closed loop consists of the following - I have a 1" bulkhead on the back of the tank, right beside the corner overflow and about 5-6" from the top of the tank. Inside the tank, I have a 90 degree street L screwed into the bulkhead, and a strainer screwed into the 90 and pointing down. On the back side of the tank is another 90 and then 1" spaflex running down to the pump, which is in the stand next to my sump.

The return from the closed loop goes straight up the back of the tank to a SCWD, then to a manifold on each side of the SCWD with 3 outputs. I have actually tried several different returns - with and without a SCWD - and it seems to make no difference. I suspect the problem is on the intake side, but I can't think what it could be. I don't think my closed loop is any different in design than what most other people run, but I haven't heard of other people having heat problems.

It's very frustrating - I'm almost to the point of just ditching the closed loop pump, plugging up the bulkhead, and adding a couple of powerheads to the tank (which is what I was trying to avoid in the first place).

[69vette]

The SCWD is adding enough backpressure to make the pumps work harder.

[mikester]

Originally posted by 69vette
The SCWD is adding enough backpressure to make the pumps work harder.

It does the same thing without the SCWD. Plus, both of my current pumps are pressure rated and should be able to handle it. In fact, there is a lot more head pressure on my sump return (chiller, UV, carbon cartridge) than the SCWD is adding, and the pumps run cool on that line.

Any more ideas?

[Aquaduck]

Yeah, i got an idea. What about the big no-no of restricting a pumps input? A 1" line into an Ampmaster 3000? You need to match the size of the pipe going in with the size of the fitting on the pump. Do you have a micro bubble problem as well? What size are your return lines?

[mikester]

You know, that's what I thought when I had the Ampmaster 3000. I even called Dolphin to make sure it wasn't a problem, and they assured me you can run it on 1" lines with a 40% loss of flow. But, the other smaller pumps shouldn't have any problem with 1" plumbing.

Here's a thought - the intake to the closed loop pump is all 1", but most of the return line is 1.25", all the way up to the SCWD, and then it's 1" on either side of the SCWD. Could the problem be that the return plumbing is larger than the intake?

[kruxy]

i think that when they say it will be fine, but with 40% less flow, they might also consider a bit of heat generation "fine" as well. did you specifically address the heat issue when you talked to them? i would say that the 1" intake line would be completely responsible for the issue. the fact that the lines are different really wouldnt change anything, it is the extra work that the pump is doing trying to suck in water (think of drinking through a cocktail straw vs. a regular one while trying to move the same volume).

[jdieck]

If you take a look at the pumps rated curve, they achieve the most efficiency when the run about the middle of the range. Too high or too low of a head will reduce their efficiency thus converting a larger portion into heat.
A pressure rated pump on a closed loop may be drawing too much flow (very little differential had pressure as the inlet and outlet are at the same level) which increases it's power consumption. If this is the case you may restrict the ouput a little bit to lower the flow to the middle of the curve.
Contrary to this if you have a restricted input the pump does not get enough flow to run at the middle of the curve (Thus the 40% reduction in flow but bet is not 40% reduction in power consumption, the difference turns into heat.). If you can try increasing the input diameter even for smaller pumps. The larger diameter of the output does not affect in this installation as it is not restricting the output.
In summary, for the smaller pumps if pressure rated you may try restricting the output, for the larger pump you need to increase the inlet pipe.

[pvtschultz]

I too agree with the too small input size. The two 90 deg elbows and the spaflex hose is going to provide a good deal of head loss for the system before the pump even gets to see the water. There for the pump needs to draw the water from the tank moreso than having the water "pushed" into the pump. I would bet that if you tried a smaller pump, you would see a reduction in operating temperature of the pump. Obviously there would be a reduction in water temperature but that could be related to the amount of work done on the water.

[cgh38]

I'm also running a ampmaster 3000 with a 4way oceans motions unit and I noticed the temp went up 3 degrees I plumbed the intake with 3ft 2" pvc with 5 elbows and 1" on the 4 outputs but 2 of them are open at random. I'm going to put a small fan to try in cooling the rear of the ampmaster hope it works

[Bozad]

One major reason pump motors run hot is due to low current. Depending on were you live, your electrical supplier may be sending low power. It happened to me. Take digital volt meter, and check the voltage at your outlet. If you voltage is less than 113 volts, this could be causing you problems. The other item is adequate cooling, pump motors need cooling around them if its placed against a wall or if its submerged and its next to the wall of the sump, it can over heat. Let me know what your voltage is.

[rufio173]

Very interesting thread. I thought if the inlet and outlet pipes were properly sized on a fan-cooled external pump, there would be no problems. Sorry to hear about your problem. I'm just glad it hasn't happened to me, but at least I've got this filed away in the memory banks in case something like this does happen.

Peace,
John H.

[mikester]

Bozad - interesting idea. I'll dig out my Fluke meter this evening and give it a shot.

I've been thinking about this some more, and there is another variable I need to investigate. I can run either pump on the return line and it runs cool, but when run on the closed loop it runs hot - but the return pump is running at the same time as well. I haven't tested just running the closed loop pump overnight with the return shut off to see if the pump still gets hot.

I suppose it's possible that running 2 pumps instead of 1 is the cause of the heat - more heat being radiated into the cabinet, more current draw, etc. I doubt this is the case - if it were the problem, then why aren't both pumps being affected - but it's worth more investigation.

[jdieck]

Of course two pumps add more heat than one.. (ahd three more than two .. He He).
Anyhow the only effective way is to measure the pumps casing temperature under while connected to one and the other circulation systems.

[mikester]

I've been tinkering around with this a little, and I had somewhat of a breakthrough. I throttled back the closed loop pump to about 60%, and this morning I woke up and the tank was at 77 - the same as when I unplugged the pump completely. Unfortunately, that wasn't enough flow, so I still have work to do, but I'm on the right track.

My suspicion is that having the return line larger than the intake line is the culprit. Come to think of it, I bumped the return line up from 1" to 1.25" when I first tried the Ampmaster, and that is when I first noticed the heat problems on the closed loop. I'm going to replace the return line with 1" line to see if that helps the problem. I'm also going to add a gate valve to the return line so I can do finer adjustments if I still need to throttle back the pump.

It will probably be a couple weeks before I get to do this, but I will let everyone know how it turns out. Thanks for all your suggestions.

[jdieck]

The best you can do is to increase the diameter of the input not the output. The valve is a good idea.

[mikester]

Originally posted by jdieck
The best you can do is to increase the diameter of the input not the output. The valve is a good idea.

I agree, but that's not feasible with this tank. I am however in the planning stages of removing my DSB, and during that process I am considering either taking the tank to have another 1" bulkhead installed in the back, or possibly replacing the whole tank with an acrylic one, which would have plenty of holes in it for closed loop intakes and returns.

Besides, if I stick with the Blueline pump for now, 1" should handle the flow pretty well. Once I add a larger intake (or more intakes) I plan on going back to the Ampmaster for the closed loop.

[jdieck]

I see, I imagined the hole diameter had something to do with it. For your future plans, unless the inlet and outlets are 11/2" to 2" try going at least one size larger than the pump inlet.
1" inlet in the pump use 11/2" to 2" 1" in the outlet, use 11/4" to 11/2".

[mikester]

Unfortunately I didn't know about proper plumbing sizing when I had my tank drilled a year ago. :(

I'm thinking about going with 2-3 1" intakes tee'd together for the Ampmaster, instead of one large 1.5-2" intake. Not only are you drawing water from different parts of the tank that way, but you also don't have to worry about the suction being too strong from a single bulkhead.

[jdieck]

The inlet is where pressure drop is most critical for centrifugal pumps.
Consider this, 2 1" lines have a cross sectional area equal to 6.3 sq. inches while a single 11/2" is 7 sq. inches. in that case use 11/4" dia which has 25% more sectional area than a 1".
I would recomend to use three 11/4" or two 11/2" joined into a 2" pipe.

Good Luck.

[kruxy]

i like to have double the draw that the pump requires, that way if a bulkhead becomes fouled or in some way obstructed, the pump can still take all the water it needs to run properly. this is also key when you have things like bta's and carpets that like to wander. if they stray close to the intake, you have a bit more time to discover them, as they are not being sucked into the intake lise a pair of lips into a soda bottle.

this on my tank meant a pair of 1 1/2 intakes, as well as a pair of 1 1/2 exhaust ports (i like to double up what can i say?).

one local reefer in the area has taught me the importance of redundency, and now everything i do is double what is suggested (except the cost of my fiancee's engagement ring, hey a guy needs live rock money i can't be spending it all on dead rock...)

[DJ88©]

Originally posted by mikester
You know, that's what I thought when I had the Ampmaster 3000. I even called Dolphin to make sure it wasn't a problem, and they assured me you can run it on 1" lines with a 40% loss of flow. But, the other smaller pumps shouldn't have any problem with 1" plumbing.

Here's a thought - the intake to the closed loop pump is all 1", but most of the return line is 1.25", all the way up to the SCWD, and then it's 1" on either side of the SCWD. Could the problem be that the return plumbing is larger than the intake?


One huge problem jumps out at me. You have restricted the intake of the ampmaster. A HUGE no no. When you spoke with Dolphin I am betting they thought you were only talking about the outlet side.

Always run at least the same size bulkhead as the intake of your pump. Never less. You are forcing your pumps to work harder thus heating up.

[69vette]

Originally posted by jdieck
Consider this, 2 1" lines have a cross sectional area equal to 6.3 sq. inches while a single 11/2" is 7 sq. inches.

I'm not sure how you came up with these numbers, but 2-1" hoses have a cross section of 1.57 sq. in.. 1-1 1/2 hose has a cross section of 1.77 sq. in..

[mikester]

Originally posted by DJ88
One huge problem jumps out at me. You have restricted the intake of the ampmaster. A HUGE no no. When you spoke with Dolphin I am betting they thought you were only talking about the outlet side.

Always run at least the same size bulkhead as the intake of your pump. Never less. You are forcing your pumps to work harder thus heating up.

When I called Dolphin, I did specifically tell them I was using 1" plumbing all around, including the intake. I guess the person I talked to was clueless, because she said it was ok.

Anyway, it's obvious to me now that the restricted intake is the problem. When I pulled the Ampmaster off a few weeks ago, I also noticed that the seal had started leaking - after only 2 months of use. Hopefully removing the substrate and going bare-bottom/starboard AND increasing the size of the closed loop intake bulkhead will solve both problems.

[mikester]

Originally posted by 69vette
I'm not sure how you came up with these numbers, but 2-1" hoses have a cross section of 1.57 sq. in.. 1-1 1/2 hose has a cross section of 1.77 sq. in..

I noticed that too. I think he calculated using the diameter, not the radius - I do that a lot too. :D

At any rate, I'm thinking about doing 3 1" intakes for the Ampmaster - that provides me with about 30% more flow than a single 1.5", so the pump should never be starved, and the suction shouldn't be as strong at any of the 3 intakes as it would be for a single larger intake.

[jdieck]

:rolleye1:
Doh...
Using diameter.... Sorry my mistake. Good it did not happen with my installation!..:lol:

[mikester]

I'm thinking about adding another 1" intake for the pump. Since I can't get another hole drilled right now, this one would have to go over the top of the tank, a la melev's design. I would tee this together with the existing 1" intake to make sure the pump gets enough flow at the intake.

Would this work, or would the pump have to work harder to pull the water over the top of the tank, negating the effect of adding more flow?

Keep in mind, this is for the Blueline pump, not the Ampmaster. Although I do want to eventually move the Ampmaster back onto my closed loop, but I will probably wait until I can do it right (bigger bulkhead, no sand to blow around and destroy seals, etc.).