40/70 pressure?

Mad Plumber

Mad Plumber

Mad Skills
Messages
248
Reaction score
7
Points
18
Website
www.terrylove.com
To begin with, I hate to sound stupid but I couldn't figure out how to post to your pump questions section. I hope you will answer my question through e-mail. I have 2 Well-X-Trol tanks,a 62gal.and a 20 gal. I have a 3/4hp sub 10gpm pump. I was running a 40/70 pressure,this way I felt the pump would not have to start as much and then would run a bit longer when it did run. I have been told lately that I should run it on a 40/60 pressure, that the 70 PSI was hard on the pump-something about the head and the seals. I really don't understand what that means exactly. Can you help me understand this better and give me some advise on whether to use the 40/60 or 40/70. This pump is sending water to 2 homes and to water some cattle as well. I just don't want to do anything to tear up my pump. Thank you for any help you can provide.
 
Someone gave you some goofy advice. 40/70 is fine. If you want the pump to last even longer, look into the Cycle Stop Valve.

bob...
 
Thanks for your reply to my question. I still don't understand about the pressure on the head of the pump. If the pump is set to cut off at 70 psi what is the actual pressure at the head of the pump? Is the pressure greater than 70 at the pump? I was also told that I would have more volume at 60 than at 70? I just don't understand how all this works. Also can you tell me how much more drawdown I would have with the 70psi versus the 60psi with the 62 and 20 gallon tanks. Thanks for the help.
 
To push the water up the well, there will be higher pressure at the pump because of the column of water sitting on top of it. The further down in the hole and the more water on top of it, the higher the pressure.

When you force water into those tanks, you are compressing a bladder (think water balloon, although designs differ). With the wider spread of pressure (30 pounds verses the typical 20), you will stretch the bladder further. This will allow it to store more water but at a price. Those larger excursions will wear out the bladder tanks faster, so you'll not only have to increased electrical costs of pumping against the higher pressure, but will be replacing the tanks more often as well. It will work, as long as your pump can ultimately reach that pressure, but your entire system won't last as long and will cost more to run.
 
The higher the pressure the pump is run at, the less drawdown gallons in the pressure tanks. That's because with higher pressure, the velocity of the water is increased. Higher velocity causes water hammer which harms plumbing etc.. Hig velocity makes the water exit your tanks and fixtures faster. That makes you use/waste more water. That makes the pump run more frequently, the additional starts reduce its life and increases the electric bill and the well must produce more water which increases its drawdown (gals removed at once; especially with two tanks!) making the water level fall farther than it would if you used less water whenever you used water. All that negatively impacts on your water quality, the life of the plumbing, the pump and the life of the well.

You would be much better off using a small pressure tank and a correctly sized CSV and run the pump at no more than say 30/50 or 40/60 psi.. Everything benefits that way. IMO pumps run at higher pressures will have more wear than those run at lower pressures, but maybe not.
 
Gary Slusser said:
The higher the pressure the pump is run at, the less drawdown gallons in the pressure tanks. That's because with higher pressure, the velocity of the water is increased.
Click to expand...

Drawdown has nothing to do with velocity of water. It has everything to do with the gas law and pressure settings. Increased start/stop difference increases available drawdown. Increasing pressure settings with the same start/stop difference decreases available drawdown.

Higher pressure can increase usage but that has nothing to do with drawdown.

Most drawdown calculations are based on constant temperature compression of air, which is not exactly correct but at least everyone is doing it the same way.

The fraction of water in the tank at any pressure P is:

Water fraction = 1 - (Pp + Pa)/(P + Pa) where:

Pa= Atmospheric pressure
Pp= Precharge pressure
Ps= Start pressure
Po= Pump off pressure

Water fraction at Pump Off = 1 - (Pp + Pa)/(Po + Pa)

Water fraction at Pump Start = 1 - (Pp + Pa)/(Ps + Pa)

So the drawdown fraction from shutoff to start again is:

Drawdown fraction = (Pp + Pa)/(Ps + Pa) - (Pp + Pa)/(Po + Pa)

Multiply the drawdown fraction by your tank volume to determine gallons of available drawdown in your tank.

I'll bet everyone told their teacher that they would never need algebra.
 
Hey bob i was wondering if you could explain the Gas Law in a little more detail. Just in case one of customers has a question about it.

Thanks,

Sam
 
Sammy, I understood it, was it more complicated than connect this pipe to the next? This is something that is important to know and explain to the customer if you are going to run any kind of business related to water and storage.

Rancher
 
Rancher, I seriously doubt that you have talked to your first prospective pump or water treatment customers yet. And here you are telling us guys in the business how to do it...

I've never lost a pump down a well but had one fall and the cable caught it. Losing one is real easy. I've been very lucky while believing that preparedness beats luck any day. I've been prepared since Cub Scout days and shortly after working on nuclear weapons and real touchy sensitive screw up once is all ya git explosives starting in the early '60s.

I knew how to fish ever since I saw my first well sticking up out of a yard, or down in a pit and knew what was in it. You seem to have trouble visualizing that.

BobNH, actually I use my memory for the common sized tanks and a chart to find the drawdown gallons of unfamiliar tank sizes, I hope that's OK instead of having to remember all those formulas you threw at me and walk around with a calculator. And really, customers don't care about *why* as long as they get a general logical description of *how*.
 
30 pounds of differential pressure will compress the bladder's air more than 20 pounds. Since you are filling the rest with water, there is more water stored in the tank.. But, because there is more water stored in the tank, you have stretched the bladder further...simple enough?
 
So it would actually be best to run a 40/60 setting? This would save me water, the life of the tanks and pump, plus save some power it takes to run the pump-correct?. When I first got this pump my installer also put in the new 20 gal Amtrol tank. At this time it was set for 40/60. It would only run for 23 seconds to fill the tank. I was told a few months later that it should run longer to prolong its life. That is when I had the 62 gal. tank installed with the 20 gal. also. I figured roughly-but not sure it is correct-that I have about 22 gal. drawdown with both tanks. With a 40/70 I think I had about 27 gallon drawdown-this is according to a chart I saw. I just thought that with the higher pressure the pump would run longer and that would benefit it and we would have more drawdown since there are 2 houses and livestock on this. I never thought about the added pressure on the pump, power consumption,etc. Thanks for your help.
 
Years ago when I was installing Well-X-Trol tanks, I almost always set the switch 40/70. The WX-201 and larger can take the extra 10 lbs. With the exception of the WX-203. This was the worse tank X-Trol ever invented in my opinion. Some of them had a dome to keep the bag from going past where it should. Some didn't. You could not get a 30 lb. differential with them. The bag would top out. If you added enough more pressure, you would certainly tear it. They also went bad quicker than most of the others. For some reason, most drillers liked that tank, so there are always a big supply of them to change out. Good for me, bad for the customer.

So; in so many words, if you want a 30 lb differential and you have a good tank (I don't remember if you said what tank you have) go for it. Or get a Cycle Stop Valve and quit worrying about cycling.

bob...
 
You don't want the pump turning on and off frequently, it needs time inbetween to cool off. Most things electrical tend to break based more on cycles than on actual running time.
 
IMO you're better off with less pressure, like 20/40, than higher. You use less water. The pump is off for a longer period of time because you get more drawdown gallons than 30/50 or 40/60 etc.. The higher the pressure, the fewer drawdown gallons. Plumbing lasts longer with less than more pressure. Same for your pressure tanks, and probably pump too. Yet 20/40 is a bit too low in today's houses with the peak demand water use with more bathrooms than in smaller homes of years gone by.

The motor of your pump is supposed to be off for at least 60 seconds before it starts again. That's for cooling of the motor and extends its life. Pump motors are rated for contiuous duty, meaning run time is unlimited. You can't have all you want and save energy at the same time. IMO the best solution is to get a CSV and get rid of your big tank and run the system at 30/50.
 
Gary Slusser said:
BobNH, actually I use my memory for the common sized tanks and a chart to find the drawdown gallons of unfamiliar tank sizes, I hope that's OK instead of having to remember all those formulas you threw at me and walk around with a calculator. And really, customers don't care about *why* as long as they get a general logical description of *how*.
Click to expand...

Gary Slusser said:
The higher the pressure the pump is run at, the less drawdown gallons in the pressure tanks. That's because with higher pressure, the velocity of the water is increased.
Click to expand...

Gary, the only reason I put the calculation there was because of your statement that I have copied again immediately above. The "That's because with higher pressure, the velocity of the water is increased." is simply not true. Also, the statement that higher pressure results in less drawdown is not correct for the example used by the original poster because he was comparing a range of 40 to 70 psi with a range of 40 to 60 psi. The 40 to 70 psi case has more available drawdown.
 
Gary Slusser said:
IMO you're better off with less pressure, like 20/40, than higher. You use less water.
Click to expand...
Gary, I guess then when I reduce my pressure switch to 0/0 I will use a lot less water...:D Please explain the coorelation between a lower pressure differential and lower water use?

Rancher
 
Gary Slusser said:
OK, so 40/70 will give him more draw down than 40/60.

But you do agree that 30/50 gets more draw down than 40/60 right?

If you agree, in layman's terms please explain why or how that happens; in layman's terms.
Click to expand...

The 30/50 setting has greater available drawdown than the 40/60 setting.

For the case where the tank is properly precharged for the "start" setting, a 30/50 setting has more available drawdown than a 40/60 setting because the air is compressed to a smaller volume in going from 30 psi to 50 psi than is the case when compressing from 40 psi to 60 psi.

Because the final "stop" volume of air is less, there is more water in the tank that can be "drawn down" before the pressure reaches 30 psi again and starts the pump.

At sea level the "air fraction at shutoff" is (start + 15 psi)/(shutoff + 15 psi); and the greatest drawdown corresponds to the smallest "air fraction at shutoff".
 
You must log in or register to reply here.

Similar threads

R
Help with a new Deep Well system.
Replies
6
Views
496
Valveman
Valveman
Cruisinforgold
Need Some Help Diagnosing this Situation with pressure and operation of well
Replies
11
Views
3K
finnski
F
K
Well pump stays on, pressure tank has no water
Replies
2
Views
487
SuperGreg
SuperGreg
Tubby
Shopping for a pressure switch; am I on the right track?
Replies
1
Views
237
Valveman
Valveman
D
Is The Pump Running Dry?
Replies
17
Views
2K
DS1
D
Back
Top