Cistern to pump plumbing

Hello.I have an 1800 gallon underground cistern for household water supply,located across the road in a unheated pole barn (my house is on a river bank). The pump is located in a crawl space under the house which makes for a very long suction line. The suction line at the tank is 1" galvanized pipe 30" long about half way up the tank. It then elbows to the house with 1-1/4" plastic to the crawl space. the pump is a Myers HR50S
shallow well jet pump with 1-1/4" inlet and 1" outlet. About 15 " from the inlet the suction line is reduced to 3/4" galvanized. Why would this be plumbed this way? I am going to replumb the piping under the house. Should I keep this configuration? Also I tried to add a foot valve at the cistern but the pump would not get it's prime. It didn't have one before so I took it back off.
The reason I am replumbing, is because it is at least 20 years old and to install vacuum gages to find out why I can only draw a few inches below where the suction pipe elbows down in the cisternand. I hope if there is leak it isn't under the asphalt road. Thanks for any info.

Very long suction lines often have a high spot in them where an air bubble can be trapped. That can make it very hard to get the pump running.

The best way to get such a line primed is to have a vent and/or priming port at the high spot. You need to get the line filled with water so water is coming out at the high spot; then close the valve.

If there is a suction leak the air will again collect at the high spot and severely reduce capacity of the suction line.

A submersible pump in the cistern is the best solution.

Bob NH said:

Very long suction lines often have a high spot in them where an air bubble can be trapped. That can make it very hard to get the pump running.

The best way to get such a line primed is to have a vent and/or priming port at the high spot. You need to get the line filled with water so water is coming out at the high spot; then close the valve.

If there is a suction leak the air will again collect at the high spot and severely reduce capacity of the suction line.

A submersible pump in the cistern is the best solution.

Click to expand...

Yes,I totally agree (pumps push better than they pull), but this system has been here for twenty years and worked okay till recently. My main question was why they rerduce down from 1-1/4" to 3/4" about 14 inches from the pump inlet.

Pump problems

I'm a little confused by your post . You state that the suction pipe running from the cistern to the crawl space is 1 1/4 inch plastic . You then state that the suction connection on the pump is reduced from 1 1/4 to 3/4 galvanised pipe . Are you sure the 3/4 isn't the outlet going to the pressure tank ? Since you don't have a foot valve in the cistern I would assume the whole system is fairly level , otherwise I think you would lose your prime . The only reason I can think of that a foot valve won't work is that your pump is pulling at it's max & adding a foot valve is the straw that breaks the camels back ( so to speak ) . If I'm not mistaken foot valves have a spring in them which must be sucked open . Anyway they hold the back pressure in the pipe & would require some force to overcome which your pump may not be able to do . I agree with the previous poster . I would just install a submersible pump in the cistern . I'm sure there are people on here that knows much more than I do so maybe some of them will chime in .

Yes,I totally agree (pumps push better than they pull), but this system has been here for twenty years and worked okay till recently.

Click to expand...

That all depends on what YOU call OK. In my book a little 1/2hp jet pump pulling through a pipe that long and bushed down as small as 3/4" surely couldn't do OK.

If you want an improvement, either replace the whole suction line with 1-1/4" pipe or larger or go with a sub in the cistern.

bob...

speedbump said:

That all depends on what YOU call OK. In my book a little 1/2hp jet pump pulling through a pipe that long and bushed down as small as 3/4" surely couldn't do OK.

If you want an improvement, either replace the whole suction line with 1-1/4" pipe or larger or go with a sub in the cistern.

bob...

Click to expand...

I am an elderly single man so I guess I mean it works to supply my needs and has for twenty years. I will replace the 3/4" reduction to 1-1/4" as you suggest but the cost of
replacing the entire line,which goes under an asphalt road and approximately 110 feet,is cost prohibitive. I likewise do not wish to replace the pump with a submersible for the same reason unless I absolutely have to. I assumme you,like myself, can think of no good reason for the reduction of the suction line at the pump.Thanks.

WV Hillbilly said:

I'm a little confused by your post . You state that the suction pipe running from the cistern to the crawl space is 1 1/4 inch plastic . You then state that the suction connection on the pump is reduced from 1 1/4 to 3/4 galvanised pipe . Are you sure the 3/4 isn't the outlet going to the pressure tank ? Since you don't have a foot valve in the cistern I would assume the whole system is fairly level , otherwise I think you would lose your prime . The only reason I can think of that a foot valve won't work is that your pump is pulling at it's max & adding a foot valve is the straw that breaks the camels back ( so to speak ) . If I'm not mistaken foot valves have a spring in them which must be sucked open . Anyway they hold the back pressure in the pipe & would require some force to overcome which your pump may not be able to do . I agree with the previous poster . I would just install a submersible pump in the cistern . I'm sure there are people on here that knows much more than I do so maybe some of them will chime in .

Click to expand...

Yes it is the suction line that is reduced from 1-1/4 plastic to 3/4" galvanized just before the pump. It does have a check valve in line just before it reduces and I replaced it which improved the level I could pump down to. A foot valve is merely another check valve with a strainer meant to be installed at the end of the suction line. If the in-line check valve is working properly it should accomplish the same purpose as the foot valve.
I do agree that the added resistance of the foot valve I installed was indeed the straw that broke the camel's back. As i replied to speedbump, I would add a submersible if I had to but hope I can get away witout doing so.Thanks.

It does have a check valve in line just before it reduces and I replaced it which improved the level I could pump down to.

Click to expand...

The right way to do this is to remove the check valve and leave the footvalve. Removing the 3/4" line and replacing with 1-1/4" would be an improvement also.

bob...

speedbump said:

The right way to do this is to remove the check valve and leave the footvalve. Removing the 3/4" line and replacing with 1-1/4" would be an improvement also.

bob...

Click to expand...

Thanks alot speedbump. Will do.