Accumulator - another pressure question

Goulds (well pump systems) says to precharge tanks 2 to 3 psi lower than pump cut-in pressure. This is with no pressure on the water side. This gives maximun drawdown.

Mary,

I'm not sure if the ShurFlo pump system will work the way you want.

For background, a typical well pump system uses a pump, a pressure tank (accumulator tank), and a pressure switch.

The pressure switch controls the pressure. These days, the switch typically is set to turn the pump on when the pressure in the tank drops to 30-40 psi, and turns the pump off when the pressure reaches 50-60 psi.

The air pressure in the tank does NOT control the water pressure. It only acts as a cushion to push against the water pressure. Typical air pressure is 5-10 psi with no water in the tank.

The typical well pump flow rate is 7 gpm or higher as needed to meet maximum flow demand. The flow is measured over the pressure range set by the pressure switch.

Now let's look at your proposed system. The switch on the ShurFlo pump appears to shut off the pump when the outlet pressure reaches 55 psi. There is no indication that the pump will start at some lower pressure, so it looks like it will start back up when you lower the pressure by opening a faucet. That's why the pump instructions say a pressure tank is not needed.

The stated volume of most pressure tanks in considerably higher than what it will deliver to service. For a 2-gallon pressure tank, the "drawdown volume" from 55 psi to 40 psi likely will be in the range of 1/2- to 3/4-gallon.

I visited the ShurFlo pump site and downloaded the pump pressure curve, which indicates the flow rate vs. outlet pressure. The rated flow of 3 gpm is delivered only when there is no pressure at the outlet. At a discharge pressure of 40 psi, the flow drops to 1.2 gpm, and at 55 psi it drops to about 0.25 gpm.

What does all this technical stuff mean to you? Let's say you want to take a shower and the low-flow showerhead delivers 1.25 gpm. When you open the faucet, the ShurFlo pump should start and deliver water at the rate of 0.25 gpm. To keep up with the shower flow, water will flow at the rate of 1 gpm from the tank. After about a minute or two, the pressure will have dropped to 40 psi. At that pressure, the pump output will have increased to 1.2 gpm, so the pressure won't drop much more.

ShurFlo makes good pumps, and I know a lot of people who are very satisfied with them. However, it doesn't look like the accumulator tank will prevent pump cycling, and the only way to predict if it will deliver more water is to look at the performance curve for your current pump.

Thanks for all the information. My accumulator holds 2 gallons. I just ordered a new Sure Flo revolution pump which is OK to use with accumulator. Plumbing will have no problem with 55 lbs.

Will be happy when the 40 psi pump is replaced.

Check whether or NOT that your pump style/design can be used with an accumulator tank!! Accumulator tanks are not recommended for use with some newer pumps.
Go to MFG. website and verify.

55 psi is not going to be a problem with your rig plumbing lines/fittings....
(unless you have really junk plumbing)

It depends... there's two types of accumulators.

The cheap ones are just an air chamber, and can become saturated and lose their air.

The better ones have a rubber bladder. Those have a Schrader valve on top. (Like a bike tire) You can adjust the pressure in the bladder to work like you want. Just raise it to match the pump's output. Those are in fact, just a miniature version of what's used in a typical well system. The pump feeds water into the system, the bladder compresses and holds pressure in the piping system. The pump now only runs to fill the volume of the bladder/tank area, and cycles much less, and also smooths out the water flow. It's especially effective for low flows, (barely open faucet) where the pump would normally fast-cycle.

The accumulator tank just allows you to use a little water without the pump cycling on and off constantly. It gives you some cushion in the system so you can usually flush a toilet in the middle of the night without the pump going on, then when the pump does run, it stays on a bit longer to build up to its balance point. They really are handy.

Suggest you check your water lines 55 pounds of pressure is a lot.
Careful you dont blow line where you cannot get to it.
Accumulator tanks are great you will have contant water no
"high/low" points, bad when you are taking a shower.
I have one and would not be without it.

The accumulator does not control the pressure, that's controlled by the pump. The accumulator does help maintain a more stable pressure though, along with minimizing the pump cycling. Changing to a higher pressure pump will work fine with the accumulator, although the air pressure will need to adjusted for optimum effectiveness and drawn down capacity.