Set Up of Centrifugal Transfer Pump

Little Giant, did you purchase this from Grainger?

If you did, call your Grainger Rep, they will help you out........... They then will connect you to the experts.

I had to install a emulsifying trash pump in our lab, that had to have at least 24 ft hd and pump it 350 feet.

Mag Drive? Why?

Little Giant pumps are OK in my experience, but I'd have gone direct drive. You may be asking too much of it.

Call their tech line.

The general idea of why I went with magnetic drive this time was to avoid leaks, but nevermind that. Also, for some strange reason I was having trouble locating some electric driven diaphragm pumps as I had purchased before for chemical transfer, but those would have done this job in spades. The only ones I found at Grainger this time are 12VDC, not 115VAC, too bad.

Operators re-circed the hot-well on the make-up line without opening the condensate tank discharge valve and totally blew the O-ring out of this pump and pinched it. I learned that the white plastic this is made of is somewhat strechy at 245 psig, but that it did not fracture as PVC would have. I "patched" the O-ring as best I could, and after learning the stud bolts that hold the pump together were stripped out of the plastic, I went and purchased some 10-24 all thread, cut four pieces to length, then carefully drilled out the holes to accept the 10-24 with a lock nut on one end, pump being held together with wing nuts, also 10-24. No more leaks under "normal" pressure.

The pump has sufficient lift to provide a useful stream of water in the laboratory, but I am still head scratching on precisely where to set the contacts of the pressure switch.

OK, nothing positive to say here. You're pumping hot water, right? Why mag/diaphragm pumps. My pool pump is 4-5 years old, runs 15-18 hours every day and doesn't leak.

Never bought pumps from Grainger. We got ours from the manufacturers. I had direct access to their engineers. One of the perks of being an OEM.

Your pump is too small. A 4 series pump runs out of steam at 20 feet of head. DC, really? Use two?

Goulds make some good SS pumps. That's what I'd use. I imagine Graingers would carry some.

The telling clue here is "operators". They can ruin a good pump in a heartbeat.

Take the operators out of the control loop and your pump will last much longer. If you can't do that, give them one button to push and tell them you'll cut their fingers off if they mess with anything.

Sorry, I'm sure you don't have the budget for my "fix".

Try two, in series. The housing is probably glass filled polypropylene.

Good luck.

You are correct. After talking to pump technical support at Grainger, here is what I found out:

(1) the pump will not have a problem operating with a cut-out pressure of 15 psi (from 24 ft suction head and 10ft of discharge head), and at 10 psi cut-in pressure, I should still be able to make the pump come on by opening the valve and only then (as long as leaks do not exist).

(2) the thing I don't get is why the pump is rated for 1 gpm at 24 ft head output, and I only get 2 LPM (1.5 gpm) at 23 ft above the pump. There again the actual head on the pump is higher under flow due to 3/8" tubing.

(3) I did find some small 110 VAC diaphragm pumps, as a cheap fall-back solution. Those have much higher pressure ratings, and will deliver the flow needed, and all have their own internal pressure switch (non-adjustable).

(4) all of the pumps I have even considered using for this are intermittant service only, not continuous duty. I still have to figure out how long I can run this motor before the thermal overload kicks in, but so far, I have not tripped it, even after about 15 minutes. I figure most times I need 7-8 minutes to fill lab carboy.

(4-1/2) Thanks for helping me scratch my noggin over this.

The company I worked for built lines with as many as 60 pumps of various types, capacities, materials, and operating conditions. Fractional to 10HP mostly. Plastic, bronze, Titanium, SS, Hasteloy, you name it. I rarely saw a pump in our shop perform exactly as specified by the manufacturer.

We tested a lot of them. Some in the test sump, lots in service. We destroyed some in the process, and our customers (operators mostly) destroyed a lot more.

When the pump curves are developed by the manufacturer, they are done under ideal conditions. In a lab.

LGI-PMP-4-MD-SC-Bulletin.pdf shows a typical pump curve for this pump. As you can see, the curve stops at 24 feet of discharge head under ideal conditions.

If you already know all of this, my apologies.

No apology needed brother. I found that same sheet yesterday evening, right before leaving for the day, and it appears to me that the pump is doing all it can do with that 75-100ft of 3/8" line on the discharge side, and pushing the water uphill 23-24 feet on top of that. 30 gph sounds very close to what I measured, giving the pump curve the benefit of the doubt, but that pump will run hot when set up that way if it runs more than about 3-4 minutes at a time. I will just put a Gralab timer on when the lab faucet is open, problem more or less avoided.

1. Close the valve.
2. Decrease the cut-out setting until the pump stops; then just a tad lower.
3. Set the cut-in a few psi lower, but still higher than the static head when the tank is empty.

If the pump can put out only 24 feet of head, conditions 2 and 3 may be incompatible.

Static head when tank is "empty" is zero. I will set it at approximately 9 pounds minimum, so that I can get the pump to start under most conditions.

A few queries.

Tank is 24 feet tall side wall, but what is water depth? If it's nearly full static head is low or even negative. Also variation in depth has to be considered.

Is the pressure switch at pump level or lab level or where?

Is there an expansion vessel? Otherwise pump will start/stop like there's no tomorrow. Doesn't have to be a big one, can have a minimum-run timer to limit pump start frequency.

yes, a capacitance tank

Incorporated into the pump?

The tank varies considerably in level when plant is online, but it does so reasonably slowly. Rarely is the tank above 100%, but at 103% it will overflow through the manhole lid on top (loose lid). The problem with the whole set-up will be not so much that tank level is changing up and down so that the cut-in condition wants to be true, but will the discharge line stay "solid" with water, and not allow air ingress by leakage. The pressure switch is no more than 12" above the pump, and that is even with supply header off the tank. If the water column pressing on the switch leaks down to a smaller value over the course of time, then the pump will start, re-pressure the line, and cut-out once again, but I do not want this to have any frequency above perhaps once/hour. To check this I would need to stand by the pump for an extended stay, or put a current logger on it. I hope the I&E guys will make themselves helpful by providing that.

I will resume testing this morning based upon settings I put forth in earlier posts to see how things behave.