That tank is an expansion tank. You need it installed to prevent the kind of thing that is happening. I believe that the pump and pressure switches are working properly.

The new pump has a check valve on it so that the water can't flow backwards and the water is expanding in the water heater when it's heated causing excessive pressure. The expansion tank solves that problem.

Does a 2 gallon expansion tank sound about right? This is a 3000 sqft home with 4 bathrooms and a 50 gallon tank.

Also, once I put the tank in what would be the max that I could safely turn the PSI up to on my pump before I am in danger of something bursting? 60 is ok but 80 is really nice for showers and doing dishes.

yes, the 2 gallon tank is typical.

Under 80 psi is the answer to your question. 60 psi is good, 70 is as high as I would consider going - I think you are stressing everything for not a good reason over 60 psi.

The answer is to stop guessing and stop asking other people to guess. Equipment specs determine allowable pressure. Period. The pressure at which you may set your booster pump is determined by calculating the overpressure that will result due to lag between the pressure switch and the pump, along with system surge and the effect of the expansion tank (if you install one).

Ok. I will keep it at 60. Should I maybe do a bigger tank than 2 gallons to account for the fact that I have both the HWH and the pump conceivably adding extra pressure to the system? Looks like going up in tank size is not much extra money.

Thanks Alice. That was really helpful.

In general, the pressure tank is determined by the size of the HWH, not that pump.

And for 4 bathrooms, 50gal seems small to me.

It should be written on the pressure relief valve at what pressure it will open. Usually around 150psi. This is not permission to up the pressure in your system. Doing that will cause water solenoids to pop open, like the dishwasher, clothes washer and refrigerator.

The valve says 150 psi. Will it start to weep before it gets to 150? Or is the puddle I am seeing likely an indication that it is getting to 150 - even if temporarily?

I do have some respect for the power of high water pressure. I had two crappy hoses outside that were mended with repair kits. When I had the pump set to 80 psi it blew open the splices on the hoses. Down to 60 it went. My wife was not happy but ...

The 50 gallon tank has been fine for the year we have been here. Both my kids are in college so 10 mos a year it's just my wife and I.

Thanks for all the responses.

You are getting closer to the 150 psi temporarily. That's really, really hard on all of your plumbing - especially the water heater. The P&T valve is the last line of defense against catastrophic tank failure. Do not allow that to continue.

Install the expansion tank and set the pressure to 60 psi. If you want to up the size from the 2 gal to the 4 gal that's fine too. It will give you just a bit more cushion. Be sure that you support the tank - particularly the larger one - properly. Thanks to oneandonlybobjones for the sizing chart - I like it when people give references.

weedmeister is correct about what the higher pressure does to things: It's hard on solenoid valves in washers, ice makers and dishwashers. It also exaggerates water hammer and stresses things like flex risers and flex hoses. Coming home to a burst washing machine hose that has been running for hours and having your furniture float out the front door when you open it is no fun.

If you don't have enough flow at 60 psi you might look at cleaning aerators and such... but in general you shouldn't expect to pressure wash the dishes from the kitchen faucet.