Well pumps question

Ok maybe you guys can help settle a disagreement. A guy at work and I argue why a well pump is down in the well. I maintain that it is because it is easier to push water witha pump than it is to suck water up. (in this area the common well depth is 100" or more). The other guy argues that it is because that way the pump doesn"t lose its prime.
I think with check valves, expansion tanks, valves there is no reason to worry about a pump losing its prime. I am sure some of you guys know more than the two of us combined, what is your thought?

Both of you are correct to a point. Even with your check valve and bladder tank and so forth the above ground pump can lose it's prime if just a tiny grain of sand or trash prevents it from closing and thus keeping the water from draining down the pipe.

Full vacuum is about 28" of mercury, which is about 31' of water column. That is the maximum that you can suck water up. The pump is in the bottom, and has to be there. This does not apply if you are dropping the water the same distance down, and the pipe always remains full.

You r right, it's easier to push water than suck water, why do u think a Honda or other pumps have a short suction hose, but a longer discharge hose? My well pump is down 230 feet. Water heads at 80, so I'm told I have 80 gallons of water in it. Not alot but it's awesome tasting water.

OK now that is the kind of scientific answer I was looking for. not saying his idea is wrong, but maybe a benefit or a side effect of what is there to deal with. Any idea where I could look on the internet to get a "engineers stamp" on that answer.

Your right as the longest column of water you can lift at sea level is 31 feet. We are at 5250ft here and it's about 24-26ft. Kind of interesting that I just had to replace one of mine. The well is 350ft with a screen at 160 to 180 and another at 300 to 320. There is a 7hp 2" pump and guess what????? There is a check/foot valve 21 feet above the pump. The static head in the case is at 38 ft. but the pull down is about 20 feet above the pump. the pump is set at 150 ft. I get 80 gpm at 120 psi.

Dam, I am long winded.
You can loose your column in a submersible without a foot/check valve. When the pump starts if there is a void in the column, you can get what they call a water hammer. It's very much like when you shut a valve off suddenly and you see the pipes jump and move around. But this kind can crater a pump. Use the check valve.

David G has it pretty correct, depends on local atmospheric pressure. Usually assume 14.9 psi which yields...

14.9/62.4*144=34.4 ft.

62.4 is the density of water in lb/ft^3 and 144 is just a unit conversion i.e. 144 in^2/ft^2.

Quick google search did not yield a site, but this is one of the first things we learn in engineering fluid dynamic classes. This is theoretical max, actual number reduced due to pipe friction and probably other things I have long since forgotten.

~Kirk

Spent another minute looking. Here is a physics site shows solution in metric, but results are same. Scroll down a ways to Practice Problem 2.
Try This

How could there be a 'void' in the outflow from a submersible pump?

You would have to pump air down the pipe to get it below the static water level.

Where would you put a foot valve when the water inlet is at the pump?

Brad

wow you lost me :>. thanks for the help. Bad part is this guy is hard headed enough to argue with the laws of physics. I don't know how you remembered that equation when I can't always remember my phone number!

The pump really doesn't suck the water up. It is pushed up by the weight of air above it. Depending on sea level, it will only work up to a certain point.

A submersible pump puts all the motor's power into pumping water to the pressure tank and loads.
A jet pump uses some of the motor's power to just keep re-circulating water through the venturi.

With respect, A siphon will not work more than the maximum lift height, the water just will not go higher in the pipe (the top of the inverted U will just be a serious vacuum, and not fill. Suction does not care what makes it, ti will not lift water more than a little over 30 feet. Jim

I was laughing my butt off when I first read this, but... I didn't know how to word what I was thinking... I had an old uncle from Montreal, he had a... dirty rhymn? In French, about ... this subject...in general, it was like - an old pump and an old hooker train of thought... anyway, yeah, pumps 'push' better than they 'pull'... but the song didn't word it that way...

Another reason for submersible pumps is usually the line is pressurized all the time so if it develops a leak it is less apt to become contaminated by the groundwater. My last well driller told me that he could not hook up a shallow well pump to a pitless adapter, even though our water table is 2ft above ground level. Another reason submersibles are popular is you don't have to listen to them, or just barely.

Another advantage of using a submersible pump is that unless the well really goes dry, the pump gets cooled by the water around it. I have seen above ground pump motors get pretty hot if they run a long time.

I had a problem with my submersible pump one time, I suppose about 10 years ago. The pump would start, run a while until the pressure switch turned it off. Then the pressure gauge would go down fairly quickly and the pump would start again, over and over. Apparently the internal check valve in the pump had failed somehow. So I pulled the pump and added an external check valve just above the pump. That fixed the problem fairly easily and a whole lot cheaper than replacing the pump. I will never put another submersible in without adding a new external check valve.

Losing prime isn"t an issue with a submersible. If there is water around the pump and the control system starts the pump, it will push water up the pipe. When I was a kid, we had a jet pump and I remember having to store several gallons of water in the pump house, in case the pump lost its prime, which it did occasionally. It was a hassle and when I was about 12, we got a new submersible. We never had almost any trouble with that pump and in talking to the woman who bought our farmstead, that pump was only replaced a couple of years ago. More than 40 years of service isn"t bad, in my opinion.