Odd sprinkler behavior (well issue?)

[plowhog]

Yesterday I started using a rainbird impluse sprinkler on a tripod. Something weird happened I cannot explain?

The sprinkler started out with good pressure. Spraying at maximum distance and "ratcheting" back and forth. All good. No other draw or demand on the water system.

20 minutes later, the sprinkler was no longer ratcheting side to side. The flow was reduced-- it was now spraying at about 75% of the former distance. I turned it off and checked the debris screen at the coupler. There was a little debris but seemingly not enough to cause a problem. Turned it back on-- once again normal pressure and normal operation. Again, no other use or demand on the water system.

20 minutes later, it was again stuck and not moving side to side. I suspected a well problem? I inspected the well and pressure there was 60lbs, which is the maximum setting. (It is set for 60hi / 40low)

I can't see the sprinkler from the well house, so I can't evaluate if it works correctly at 60psi but not 40psi? This is the same sprinkler on the same hose bib using the same hose as last year when it worked fine?

I'm stumped ... ideas?

 

[sandman2234]

Thinking that as you run the sprinkler, the level of the water in the well drops after 20 minutes which increases the head pressure (work required to pick up the water out of the well) Pumps dont like to pull water out of a well, and push it a lot better.
Course all of this is garbage if you have a submersible pump.
David from jax

 

[CloverKnollFarms]

Is the hose bib on your home? You likely have a pressure tank. It's not uncommon as the pressure is bled off through long use, the pressure drops until the pump turns on again. When it does, pressure increases again. The larger the pressure tank, the longer the interval.

We have an 80 gallon pressure tank, and our daily use is about 60 gallons, so our well pump runs about once or twice per day.

In a home well situation, there should be a pressure tank, so your well pump isn't required to run every time you open a faucet. Maybe an issue with the pressure tank?

 

[plowhog]

Maybe an issue with the pressure tank?

Hmmm ... maybe I need to check the pressure in the pressure tank. As I recall it is supposed to have something like 30psi. Maybe it bled down?

 

[steve tym]

The air charge in the tank should be two psi less than the turn on pressure. When the system is off and the tank is drained.
That's not the issue.

 

[plowhog]

I will do some further investigation and testing on this. I am still stumped why the well pressure looks normal at the gauge, but the sprinkler starts out "full bore" then declines after a period of operation.

The obvious guess is water usage or demand somewhere else, but I am confident there is no change with that. Still a mystery.

 

[triptester]

Impluse sprinklers have a minimum pressure and flow needed to operate properly. Ha the same problem. I have both city and well water available my impluse sprinklers would not function properly with the well, when switched to the cityhose bib the sprinklers worked as they sould.

 

[plowhog]

Well, I got back to my CA property, tried the tripod sprinkler again, got the same problem, but figured it out.

Once again, the sprinkler started fine. But this time it was even worse, fairly quickly dwindling down to just a short stream of water coming out a few feet. To test whether the well needed to build pressure, I stayed at the sprinkler, kinked the hose near the sprinkler, and held it kinked (off) for several minutes. To let well pressure build if needed. I let the kink out of it and no change-- just a short stream of water. Hmmm.

I swapped in a different tripod sprinkler. Works great, no problems, no pressure drawdown. So-- something is funky with that particular tripod sprinkler. Of course it worked fine last year, but it did sit all winter. I have no idea what ... inside ... the sprinkler could do that but when I get time I will tear into it and look at it. Probably start with just putting a new impulse sprinkler on top of the tripod since it almost certainly is something in the sprinkler itself.

 

[plowhog]

Thought I would update since problems returned.

I discovered the pressure in the bladder tank, with all lines drained, was zero. Hmmmm. So I pressurized it to 38psi, since our well cut-in is 40psi.

Everything started working normally again. I think the "dead" bladder tank was behaving like a partial obstruction or limiter on pump pressure.

Now of course: why did the bladder pressure go to zero? (I just replaced it two years ago.)

 

[Valveman]

Thought I would update since problems returned.

I discovered the pressure in the bladder tank, with all lines drained, was zero. Hmmmm. So I pressurized it to 38psi, since our well cut-in is 40psi.

Everything started working normally again. I think the "dead" bladder tank was behaving like a partial obstruction or limiter on pump pressure.

Now of course: why did the bladder pressure go to zero? (I just replaced it two years ago.)

Sorry I missed this. Nearly every problem with a well or booster pump is caused by the pump cycling on and off too much. An 80 gallon size pressure tank only holds 20 gallons of water. If there is no irrigation and the house only uses 60 gallons a day, that is only three times a day the pump will need to cycle. But an average house uses 300 gallons a day and many have irrigation, heat pumps, or other long term uses of water.

Running a single sprinkler is the worst thing you can do to a pump system. The pump is producing 10 to 20 gallons per minute, depending on the size of pump, and a single sprinkler is only using about 3 GPM. Even with a huge 80 gallon tank (20 gallon draw) a 3 GPM sprinkler will drain the tank every 6 minutes and the pump will refill the tank in 1 minute. That is a cycle every 7 minutes. Doesn't sound like much but it adds up. 8 cycles and hour is 200 cycles a day, or 73,000 per year of use.

Every time the pump cycles on the pump, motor, pressure switch, control box, check valve and everything else in the pump system maxes out. Even shutting off from a full flow condition is a shock to the entire system. The bladder/diaphragm in the tank also goes up and down with each pump cycle. It is like bending a wire back and forth until the diaphragm breaks, which is how the air gets out of a 2 year old tank.

Once the tank is bad (waterlogged) the pump will cycle rapidly. 200 average cycles a day becomes 2000 quick cycles. This causes the overload in the motor to trip, shutting off the pump. The overload auto resets in a minute or so, which makes it look like the sprinkler is just weak. A few days of the overload resetting itself and you are going to need a new pump while you are replacing the tank. This is all by pump/tank manufacturers design to plan the life of a pump system to last an average of 7 years. Some last longer, some shorter, but the average is spot on 7 years.

Doubling or tripling the size of the pressure tank recommended by the manufacturers can greatly lengthen the life of a pump system. Using something that basically eliminates cycling like a Cycle Stop Valve will make pump systems last even longer than that, without needing a large pressure tank.

Without a Cycle Stop Valve to vary the flow from the pump, the only way to make a 10 GPM pump run continuously is to always use 10 GPM (at least three, 3 GPM sprinklers, never 1 or 2). With a 20 GPM pump that would take about 7 sprinklers at a time to save the pump. A CSV will let you run one sprinkler at time, make the sprinkler shoot further, and extend the life of the pump and tank at the same time.