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jenkell · Jul 29, 2011, 04:48 AM

For some time I have noticed that there is a strange noise emanating from the pressure switch on my system. Water pressure in the house is lower than average - but that may be due to low flow faucets. Decided to check pressure in tank. It reads 60 psi!
Pressure switch is set for 40 psi, and instructions on tank suggest 18 psi as correct pressure. As I already have low pressure at faucets I have left as is pending advice from an expert.
If I bring the pressure down to recommended will this reduce pressure at taps even further?
What other changes can I expect?

hkstroud · Jul 29, 2011, 05:13 AM

The suggested tank pressure is the pressure you establish in your tank (empty) when setting up your pump switch. Tank pressure is set to 2 lbs. below your pump cut on pressure. That way your pump comes on just before the tank is empty. It does not affect your water pressure.

If you pump switch is set to 40-60 lbs. your tank pressure should be set to 38 lbs. Having your tank pressurized to 18 lbs. only means your pump comes on a little before it has to. Some people prefer a 30-50 setting. I prefer a 40-60 setting.

Turn off breakers, empty tank and pressurize to 38 lbs. Turn breakers back on.

jenkell · Jul 29, 2011, 04:33 PM

Thanks for the advice, Harold.
One question remains. Pressure tank maker recommends a pressure of 18 psi with cut off switch set to 40/60 You suggest 38 psi . If I understand your previous advice properly, the lower I set the tank pressure, the greater the usable water volume becomes

hkstroud · Jul 29, 2011, 05:41 PM

No. It actually means less usable water. The tank pressure is set in conjunction with the switch settings. It is a bit involved to explain but it amounts to you have a certain amount of water in the tank taking up space that will not be used as long as the pump comes on as it should. If the tank is properly pressurized, that space is taken up by air. When the pump comes on that air can be compressed, resulting in a greater volume of usable water. A complete explanation is a bit in long but if you would like I'll post it.
I don't know why a tank manufacturer would have a recommended tank pressure. Eighteen pounds would only be correct if the pump switch settings were 20-40 lbs.

jenkell · Jul 30, 2011, 03:26 AM

Thanks Harold. I can see the reasoning, and will try setting as you suggested. By the way, if I were to reduce the pressure without draining tank down (but turning off power) would that work OK? If not, can you explain why. And yes, I would appreciate it if you were to post the complete explanation. I hope its not too much trouble.
Frank

jlisenbe · Jul 30, 2011, 03:41 AM

Try this link. Lot of good info.

Bladder Type Water Storage & Pressure Tanks - Diagnosis & Repair

The recommendation of 18# bladder pressure would be, I would think, with the assumption that your switch is set to 20/40. HK is entirely correct that 38# is what you want at 40/60. It must be set with the system off and drained.

Handyman2007 · Jul 30, 2011, 05:28 AM

You have to find out why the tank bladder pressure is only 18 lbs. The tank may have a leak in the air valve allowing the air pressure to bleed down. I would drain the system, pressurize the bladder to 38 lbs. wait for an hour then recheck the pressure before turning the system back on. If the pressure bleeds down, then the tank may need replacement.

hkstroud · Jul 30, 2011, 06:12 AM

OK, lets say you have a pressure tank. Not a bladder tank. Pressure tanks are usually galvanized. Bladder tanks are usually painted. If you take a sealed tank, any size, but lets pretend we have a 100-gallon tank. When you begin pumping water into the tank you compress the air. When the tank is approximately 1/3 full or water or approximately 33 gallons, the compressed air will exert approximately 40 lbs of pressure on the water. Note that you cannot compress water. You now have 33 gallons of water and 66 gallons of air. When you pump in another 1/3 tank of water or another 33 gallons, the air is further compressed and will exert approximately 60 lbs of pressure on the water. You now have 66 gallons of water and 33 gallons of air. Note also, that you reduced the volume of the 40 lb. air to one half its volume. That is, one half the volume it was at 40lbs.

You now have an acceptable pressure minimum and maximum and you have an acceptable pressure differential of 20 lbs. You tank has the maximum amount of stored water for those pressure settings. You have 33 gallons of “usable” water. The first 33 gallons is used to create the required 40 lbs of pressure. The next 33 gallons is your usable water and the final 33 gallons (of space) is the compressed air.

The only problem with pressure tanks is that water will absorb some of the air in the tank. With less air it takes more water to reach the minimum pressure. With a smaller volume of air you reach your maximum pressure quicker. As this process continues all of the air is absorbed by the water and your tank is “water logged”. The use of a small amount of water will cause a dramatic drop in pressure. As soon as the pump comes on and a small amount of water is added, there is a dramatic increase in pressure and the pump shuts off. This is known as “short cycling”. Short cycling decreases the life of the pump.

When your pressure tank becomes water logged, you turn off the system, drain the tank while letting air in and start over again. How often you have to do this depends on the size of the tank and the amount of water used over a period. There are automatic air control valves that can be put on a pressure tank but they don't seem to work very well, very long.

A bladder tank does two things for you. The bladder keeps the air and water masses separate so that the air is not absorbed by the water and they increase the usable storage capacity of the tank.

They increase the usable storage by allowing you to pressurized the tank. Remember back, I said that when you when you went from a 1/3 tank of water at 40 lbs of pressure to 2/3 tank of water at 60 lbs of pressure you decreased the air volume by one half. That one half was 33 gallons.

Take the same 100 gallon tank with a bladder. Pressurized to 40 lbs. You should probably also note that when you pressurized the tank you are putting air between the tank and the bladder, not in the bladder. Now in order to compress that 40 lb. air to one half its volume you need 50 gallons of water. So you have 50 gallons of usable water between the desired 40 and 60 lb. pressure ranges.

That's my logic. I admit that if you look at the usable storage of bladder tanks the numbers don't quite add up. Frankly I don't know why not. Perhaps, partly because of the bulk of the bladder or the fact that different people like different pressure settings. Perhaps my volume and pressure numbers are slightly off. Note that I always said approximately. The number would certainly vary with different atmospheric air pressures. Be huge differences between sea level and Pike's Peak. However, the logic is still valid.

So all this come back to if your tank pressure less than it should be relative to the pump switch settings you are using a certain volume of water to bring up the pressure to the minimum 40 lb. of the switch setting. That volume of water cannot be compressed. If an equivalent volume of 38 lb air is used, it can be further compressed on the way to 60 lbs and therefore give you more usable storage.

Admittedly you will probably never notice the difference in a small tank. I have an 1800-gallon tank. Pressure tank of course, I don't think bladder tanks are made that big. It takes 600 gallons to get up to 40 lbs of pressure.

If you think this was long and verbose, think about how long it took me to key it in.

jenkell · Jul 30, 2011, 12:59 PM

Many thanks Harold. And thanks for spending the time to put this up. It will take me a while to fully digest it!
I am beginning to think that the 60 psi pressure I worried about on my tank may be normal, as the reading was observed with the tank fully pressurized and pressure switch set at 40/60. No water spews out, so bladder is likely fine. Perhaps when I drain it down and check it will indeed be at the 38 psi pressure you advise. By the way the discrepancy that you note could very well be related to inevitable inaccuracies inherent in measuring instruments

jenkell · Jul 30, 2011, 01:05 PM

Originally Posted by Handyman2007

You have to find out why the tank bladder pressure is only 18 lbs. The tank may have a leak in the air valve allowing the air pressure to bleed down. I would drain the system, pressurize the bladder to 38 lbs. wait for an hour then recheck the pressure before turning the system back on. If the pressure bleeds down, then the tank may need replacement.

Thanks for your comment. The tank pressure is actually 60 psi. I was worried that it was too high. Harold advises correctly that the EMPTY tank should be pressurized to 38 psi, and I will do that.
Frank