Delay from when pressure switch clicks and pump turns on

LLigetfa said:

If the OP has a deep enough well and the static water table is low there can be a lot of pipe under vacuum.

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All the drop pipe will be under vacuum, from the upper check valve almost to the pump. But if there is no hole in the upper pipes to let air in, there will be no void or empty space in the pipe to refill. If the vacuum is strong enough, I guess you might pull a few air bubbles out of the water. This could make a small air space at the top, but it couldn’t be more than a cup or so. When even a 10 GPM pump comes on, it will pump a cup in a split second, the void will be refilled, and water will be flowing out the top of the well almost instantly.

Pumping 30 seconds at 10 GPM before water flows from the top of the well means there is a 5 gallon void. 5 gallons would probably fill the entire line of drop pipe. So I think the water is draining to the static level. I just don’t know where the air is getting out.

valveman said:

All the drop pipe will be under vacuum, from the upper check valve almost to the pump. But if there is no hole in the upper pipes to let air in, there will be no void or empty space in the pipe to refill. If the vacuum is strong enough, I guess you might pull a few air bubbles out of the water.

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Ummm... NO. the water column will fall to within about 30 feet from the static water table so if his water table is 130 feet below the topside checkvalve, the top 100 feet of pipe will have a vacuum and will not have water in it. When the pump comes on, it needs to fill that 100 feet of pipe.

It works just like a mercury barometer except that mercury is heavier so you don't need as tall of a column as you do with water.

valveman said:

Pumping 30 seconds at 10 GPM before water flows from the top of the well means there is a 5 gallon void. 5 gallons would probably fill the entire line of drop pipe. So I think the water is draining to the static level. I just don’t know where the air is getting out.

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We only know the depth the pump is at. We don't know the depth to the water table. We also don't know the size of the drop pipe. We can only assume 10 GPM.

Initially the OP said 10 seconds... later he said 30. Maybe all the upthrust on the impellers from the pump starting without any head exacted its toll on it already and it can no longer put out 10 GPM.

LLigetfa said:

Ummm... NO. the water column will fall to within about 30 feet from the static water table so if his water table is 130 feet below the topside checkvalve, the top 100 feet of pipe will have a vacuum and will not have water in it. When the pump comes on, it needs to fill that 100 feet of pipe.

It works just like a mercury barometer except that mercury is heavier so you don't need as tall of a column as you do with water.

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I guess I need a clear straw about 130’ long to see what you are talking about. I would bet that if the straw was full of water and I placed my thumb on top, the straw would still be full of water except for maybe the top 6” or so. But I don’t know how to figure that.

I have seen many wells holding vacuum from hundreds of feet deep. When you open a ball valve at the top of the well the vacuum is so strong it could suck your arm in easily. It can whistle so loud it hurts your ears. But I can also hear the pump running backwards and see the water level in the well rise. This makes me think the water did not fall out the bottom of the pipe until I opened the ball valve at the top. This is the same thing I see with a straw in my glass of tea.

I also know from experience that when you start a pump when the drop pipe is under vacuum, the water hammer thump hitting the above ground check valve happens within a second. Some of these wells had 3” or 4” drop pipe maybe 1,000’ feet deep. Even with a 100 GPM pump you would wait a long time for water to hit the surface the first time you turned on the pump. So long in fact that we use to keep putting our hand over the pipe while the air was being pushed out, just to make sure the pump was still running. But if you didn’t open a ball valve and let the air in, turning on the pump meant water would hit the above ground check valve almost instantly. With a good check valve up top and a bad one at the bottom, you have a very strong vacuum, but a very small void in the pipe to refill.

I would be curious to know how strong a vacuum it would take to make a 1 gallon size void?

I guess I need a clear straw about 130’ long to see what you are talking about. I would bet that if the straw was full of water and I placed my thumb on top, the straw would still be full of water except for maybe the top 6” or so. But I don’t know how to figure that.

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The equation is heavily modified by the fact that maybe 100' of that straw is underwater.

The 130' straw with an open bottom will eventually drain by displacement of air up one side of the tube. I know, I make wine. The good barrel "wine thieves" all have a check valve on the bottom, with a point to touch the bottom of your glass with.

I'm surprised that you professional pump men somehow think the laws of physics don't apply here. It is the very same law of physics that limit the lift of a shallow well pump.

The example I provided of the mercury barometer applies as well to water. The only difference is the weight. Whereas with mercury you only need a 30 inch tall column because it's so heavy, a column of water needs to be around 30 feet.

LLigetfa said:

We only know the depth the pump is at. We don't know the depth to the water table. We also don't know the size of the drop pipe. We can only assume 10 GPM.

Initially the OP said 10 seconds... later he said 30. Maybe all the upthrust on the impellers from the pump starting without any head exacted its toll on it already and it can no longer put out 10 GPM.

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I timed it over the weekend with a stopwatch. It took 31 seconds from when the pressure switch cut in to when the pressure started to rise and 114 seconds for the pressure switch to cut out at 62 psi with an 80 gal tank. No water was being used from the time of cut in to cut out.

Correction: 31 seconds to pressure and 74 seconds to cut out. My stopwatch read 1 min 45 seconds total, I miscalculated using 145 seconds instead of 95 sec.

Another slight problem is that in my infinite wisdom I built and really nice well house around the pump and tank and my landscaping doesn't lend itself to getting a truck back to it. I did construct the well house so it can be dismantled in parts. I have seen a few youtube videos of portable pullers. Is that a standard piece of equipment for repair companies nowadays?

LLigetfa

The vacuum in the pipe is interesting. Doesn't water evaporate in perfect vacuum? Interesting equation for figuring the time required to pump a vacuum aided waterhead of so many feet. To bad I don't know all the specs, might be able to determine if the pump is failing.

Bobo said:

The vacuum in the pipe is interesting. Doesn't water evaporate in perfect vacuum? Interesting equation for figuring the time required to pump a vacuum aided waterhead of so many feet. To bad I don't know all the specs, might be able to determine if the pump is failing.

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Probably be better to calculate the time from cut in to cut out since that would be when the pump is operating in the proper context.

Since it looks like you may be updating everything you may want to consider adding a Cycle Stop Valve http://www.cyclestopvalves.com. It will stop the cycling and extend the life of everythinng plus give you constant pressure!

Bobo said:

Doesn't water evaporate in perfect vacuum?

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Correct. There cannot be a perfect vacuum because of that. Still, it is like the expansion and contraction of steam. The evaporated water in the near vacuum occupies the space.

Do you know for sure where and how many checkvalves there are? The reason I ask is that if there is only one topside that you can remove without having to pull the pump, there is a distinct possibility of resurrecting the failing one in the pump. The checkvalve holds better if it has pressure against it so it might seal if it is the only one.

Also, if the pressure then won't hold it may suggest that there is a hole in the pipe.

Porky said:

Since it looks like you may be updating everything you may want to consider adding a Cycle Stop Valve http://www.cyclestopvalves.com. It will stop the cycling and extend the life of everythinng plus give you constant pressure!

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Absolutely. I was checking out the website. Makes sense to me. I too would have guessed that the pump would be using more power when choked. I tested a Physicist here at work with that question but he got it right.

LLigetfa said:

Correct. There cannot be a perfect vacuum because of that. Still, it is like the expansion and contraction of steam. The evaporated water in the near vacuum occupies the space.

Do you know for sure where and how many checkvalves there are? The reason I ask is that if there is only one topside that you can remove without having to pull the pump, there is a distinct possibility of resurrecting the failing one in the pump. The checkvalve holds better if it has pressure against it so it might seal if it is the only one.

Also, if the pressure then won't hold it may suggest that there is a hole in the pipe.

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I'm not sure of the number of checkvalves. As you may have guessed I'm not super familiar with these systems. On the very top of the well is a big brass elbow with a pressure relief on the top. Is that possibly a checkvalve? Only other big brass fitting is where the pressure switch and gauge thread into.

There could be a checkvalve somewhere on the drop pipe or even buried between the well and the house. Tee in a pressure gauge where the PRV is and see what it has to say.

Also, watch/listen for any sign of waterhammer and/or any other noise at the wellhead. Unless valveman is spot on and there is a small hole letting in air and slowly letting it back out, you should see some evidence of waterhammer if the issue is checkvalve failure.

You might want to get a pumpman or wellman on-site to render an opinion and then plan accordingly.

LLigetfa said:

I'm surprised that you professional pump men somehow think the laws of physics don't apply here. It is the very same law of physics that limit the lift of a shallow well pump.

The example I provided of the mercury barometer applies as well to water. The only difference is the weight. Whereas with mercury you only need a 30 inch tall column because it's so heavy, a column of water needs to be around 30 feet.

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I am not arguing with the laws of physics. I know the vacuum will produce a void. I just don’t think it is very big. The size of the vacuum void would determine how much water drops out the pump at the bottom. This would also determine how much water the pump has to produce to refill the void.

The fact that the pipe is under a vacuum means the pump will fill this void faster than if there is no vacuum. So if the pipe is under a vacuum, the pump should not have to run 10 or 30 seconds to refill the pipe. But if the check valve at the bottom is bad and there is a hole in the upper section of the pipe, it would take a while to refill the pipe, the same as it does the first time the pump is started when the pipe is empty.

The “big brass fitting†where the pressure switch and gauge are connected is a check valve. You can pull the guts out of this check valve and still use it as a place to screw in the pressure switch and gauge.

valveman said:

The “big brass fitting” where the pressure switch and gauge are connected is a check valve.

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If it looks like this and not a conventional tank Tee, I concur.


The following is a tank Tee.

LLigetfa said:

If it looks like this and not a conventional tank Tee, I concur.

The following is a tank Tee.

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It looks like the first one except the threads for the switch and gauge are 90 degrees apart.

If I remove the checkvalve on top and bottom checkvalves fails, won't that suck the bladder in the tank for another 14.7 psia in the opposite direction?

LLigetfa said:

There could be a checkvalve somewhere on the drop pipe or even buried between the well and the house. Tee in a pressure gauge where the PRV is and see what it has to say.

Also, watch/listen for any sign of waterhammer and/or any other noise at the wellhead. Unless valveman is spot on and there is a small hole letting in air and slowly letting it back out, you should see some evidence of waterhammer if the issue is checkvalve failure.

You might want to get a pumpman or wellman on-site to render an opinion and then plan accordingly.

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I have spent a lot of time sitting and watching the cycle. Everything is quite until the 30 sec mark when I hear the inrush of water but no visible shock or release of air can be heard. Sometimes I hear a bloup in the tank when near full but I have never noticed any air from the faucets.

I'm calling around to see if any of the wellman have a portable puller since I have made it difficult to get a truck to the pump house.

Have you put an ammeter on the circuit to see what the pump is drawing during that first 30 seconds?

The sound at the tank when it is nearly full is likely the bladder sticking and then slipping on the inside of the tank. As for air if there is any, if you have a softener and/or iron filter, it could act as an air accumulator that then purges when backwashed.