I have a grundfos sqe constant pressure well system that provides water to my house along with my irrigation system. This is combined with a 2 gallon pressure tank. We used to have a larger pressure tank with the system, but that caused issues with the constant pressure, so our well company replaced the tank with a properly sized one and now the system works great. The only issue is that when the irrigation system turns on, there is so much water leaving the house at such a fast rate, that we lose all pressure in the home for 5-10 seconds. Is this okay for my plumbing to endure these drastic pressure changes, or is there something that I should do to fix/prevent this? Are there any solutions out there? Perhaps a slow open master valve for the main line?
Pressure Decrease
- Thread starter Collin E
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Tim in Fort Worth
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If it were me I would set the timer for the irrigation system to cycle late at night when everyone is sleeping, and finish before the first person wakes up and is likely to use water. But that said, a 2 gallon pressure tanks seems pretty small for what you describe. How big was the larger pressure tank?
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My old tank was 20 gallons, but would cycle on and off constantly. The new tank is the manufacturer recommended size.
Tim in Fort Worth
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Something seems strange about a 2 gallon tank being the recommended size for the application you described. You have three serious variables in play here: Household water supply, irrigation water supply and water pressure. I'm not an irrigation expert by any measure, but I think an average irrigation system could drain a 2 gallon pressure tank in seconds, and then it's just the GPM the well pump is providing that lets it catch up after that 5-10 second gap. For the moment, leave the household water out of the equation and look at the water pressure and irrigation system. What is the constant pressure you are supposed to be maintaining? How many sprinkler heads per zone (actually Zone 1 since that's where the irrigation system probably starts its cycle), and how many gallons per minute gets pushed through those heads? I just finished installing a Hunter rotor and am looking at the chart right now. The PGP Red Standard Nozzle, at a water pressure of 50 PSI (it's the figure in bold, with the other choices 30, 40 and 60 PSI) pushes between .7 GPM and 12.7 GPM out the hole depending on the nozzle choice. Let's round the lower number up to 1 GPM to make the math easier. If you have 10 heads in the zone you are pushing 10 GPM out the hole. In 30 seconds that's 5 GPM and in 15 seconds that's 2.5 GPM. So even at 1 GPM per head it's close to draining the tank in the initial 15 seconds. If your water pressure is set to 60 PSI the numbers range from .8 GPM to 14.1 GPM.
Our pressure is set to 70 psi. Pump can do about 22. We have six heads on each zone, all have 2.5 gpm nozzles, which at the pressure we’re at push around 2.9 gpm.
Tim in Fort Worth
Member
Well, the numbers for that are 15 GPM, which works out to 7.5 gallons in 30 seconds, 3.75 gallons in 15 seconds and 1.875 gallons in 7.5 seconds. After 7 seconds that leaves .125 gallons in the tank, plus what the pump can offset. But there is another factor to consider in the irrigation system, as well. The charged lines feeding the valve are always full of water to the inlet side of the valve. But the lines from the outlet side of the valve to the sprinkler heads get depleted to some extent when the system shuts off and the lines drain because of residual pressure and gravity. When the system activates you get a blast of air from the sprinkler heads when the valves open, followed by the residual water between the outlet side of the valve and the sprinkler heads. Then you get the water that is being pushed through the valve, which is getting it from the charged lines, which get it from the pressure tank. Between what is going out the sprinkler heads and pushed from the pressure tank into the system I'm still thinking that can add up to a lot more than the 2 gallons (plus pump addition) available in the pressure
If your pump can do 22 GPM, that means 11 gallons in 30 seconds, 5.5 gallons in 15 seconds and 2.75 gallons in 7.5 seconds. In terms of time, that seems like it would account for the 5-10 seconds it takes for your whole water system to recover when the irrigation system fires up.
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Tim in Fort Worth
Member
I think the general consensus would be that any sudden jolts or pressure changes are not good for plumbing. How "not good" that is depends on if your plumbing is threaded galvanized, sweated copper, PEX or PVC. Whenever I have to cut off my water to do something I always open one outside spigot and the hot and cold water spigots on the bathtub to minimize shocks to the system, and to facilitate flushing out any sediments and debris.
A 2 gallon size pressure tank only holds 0.5 gallons of water. That SQE pump takes 5 seconds to get started. That 0.5 gallons needs to last long enough for the pump to get started. Reducing the air chare from 50 to about 30 will make the tank supply water for an extra second or three. Might be enough to help.
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