12v and manual pump from the same water source

[bluecolumbia]

hi

i'm trying to make some improvements to my fresh water system and i'm running into an unexpected problem.

my fresh water source (tank) goes to a tee, each side goes through a shutoff valve, and then a check valve, and then one side feeds the 12v pump (jabsco) and the other side feeds a whale flipper pump. the 12v pump feeds an accumulator, so the 12v pump runs intermittently. it all works fine, except that...

when both of the shutoff valves are open, during the 12v pump cycles, some water is pushed out of the manual pump each time the 12v pump cuts out. it seems like when the 12v pump stops it causes a pressure surge on the upstream side.

is there any way to resolve this? (other than shutting off the manual pump when the electrical pump is in use?)

i wasn't sure if multiple pumps from the same source would work... i figured there might be pressure loss (which is why i used check valves). i didn't expect there to be a pressure surge.

thank you for any advice

[HeywoodJ]

Generally speaking, to be expected. When the pump stops the water in the suction piping between the tank and the pump is moving and has to come to a stop. This does create a relatively small pressure surge/water hammer. Since the manual pump offers a way out that’s what happens.

In the pump world a variable speed pump that slows down gradually before stopping would do the trick, but that’s a bit overkill for a boat (there are some variable speed pumps available, but they seem to have mixed reviews). You could try a water hammer arrester on the suction side, but the pressure to exit the manual pump is so low that I doubt it would do the trick.

Curious to see if anyone else has a viable solution.

[Uncle Bob]

Originally Posted by HeywoodJ

Generally speaking, to be expected. When the pump stops the water in the suction piping between the tank and the pump is moving and has to come to a stop. This does create a relatively small pressure surge/water hammer. Since the manual pump offers a way out that’s what happens.

In the pump world a variable speed pump that slows down gradually before stopping would do the trick, but that’s a bit overkill for a boat (there are some variable speed pumps available, but they seem to have mixed reviews). You could try a water hammer arrester on the suction side, but the pressure to exit the manual pump is so low that I doubt it would do the trick.

Curious to see if anyone else has a viable solution.

Perhaps if the non return for the 12 volt pump was on the suction side it would reduce or eliminate the problem.

[bluecolumbia]

thank you so much for the replies i guess i can live with it now that i know what is happening.