Distinguishing between static water pressure, dynamic water pressure, and water flow rate can help diagnose water problems in a building. Here we explain these concepts and we describe how to measure water pressure and flow at a property where either municipal water supply or a private well and pump water supply is in use.
The water pressure regulator setting [public water supply] may not be the same as the water pressure you'll actually get in the building.
Depending on the size of the building, its piping size and length of piping runs, and the number of fixtures and number of occupants (and similar variables) in a building, it is possible to draw water out of the building supply piping at such a high rate that the overall building water pressure drops considerably below the pressure setting at the water pressure regulator.
The water pressure settings on your [private water supply] well pump pressure control switch may not be the same as the water pressure you'll actually get in the building. Similarly, the private well pressure control switch settings define the maximum and minimum water pressure you may see in the system, not the water pressure you'll see at any given moment when water is being run.
Even if every component of the private well, water pump, and water pressure tank and plumbing system are working normally, water pressure in such a building will fall between the time water is turned on and the time that the well pump is turned on by the pressure switch.
Number of plumbing fixtures being run at once: With a municipal water supply as well as private well water supply systems, the building water pressure seen at any individual plumbing fixture will vary depending on how many fixtures are being run. We tend to see this effect more on private well water systems where the total water supply system flow rate may be more limited.
Variation in municipal water delivery pressure: the municipal water system pressure may vary in the street as well as a function of level of water use in the whole community or when work is being done on the system.
Variation in small community water systems and private well pump water delivery pressure: with a small community well system as with private well and pump water supply, water pressure will also vary depending on the water pump on and off cycle and possibly on the ability of the well to deliver water.
For example, if you turn on water at a sink just after the well pump has cut out the building water pressure will be at its "cut out" pressure maximum, typically 40 psi or 50 psi. But if water has been run in the building to drop water pressure in the system to just a bit above the water pressure control's "cut in" pressure, then the water pressure observed will be lower, perhaps just above 20 psi. Details are
at PUMP PRESSURE CONTROL ADJUSTMENT.
Water pipe diameter, length, elbows and bends: Water flow rate in a building also depends on the diameter, length, and number of bends or valves in the piping system. And if water pipes become clogged with mineral deposits or debris, the water flow rate will diminish in the building, even if the static water pressure remains high.
See DEFINE STATIC WATER PRESSURE
Technical note: The D'Arcy-Weisbach equation for pressure and head loss can be used to calculate the actual water pressure loss due to friction in a building piping system. The Engineering Toolbox provides the D'Arcy-Weisbach formula: Δp =λ (l / dh) (ρ v2 / 2) where
Δp= pressure loss (Pa, N/m2), and
l= length of duct or pipe (m) and
dh= hydraulic diameter (m) and finally, ρ = density (kg/m3).
But keep in mind that even this apparently accurate calculation of the effect of piping on water pressure loss will not include the effects of obstructions in building water piping such as mineral deposits, debris, or blobs of solder from an improperly-soldered copper pipe connection.
Clogged water pipes reduce water flow rate, not water pressure.
Variations in building occupancy levels: Where building demand for water flow varies widely, a single pressure reducing valve may not be able to handle the maximum water demand flow rate. This condition occurs at buildings where there is a large water supply main to an apartment or office building whose water demand can vary enormously (0.5 gpm to 100 gpm) depending on the building occupants. Watts and other pressure reducing valve producers recommend a nice solution to this problem.
As we explain
atWATER PRESSURE REDUCER / REGULATOR, parallel pressure reducing valves are sometimes installed to correct this difficulty. One pressure regulator control is set at a higher psi flow rate than the other. For example installing a Watts Model 223 pressure reducer set at 50 psi in parallel with a second Watts 223 pressure reducer set to 60 psi will allow increased total water flow capacity during periods of peak water demand.
A failed hot water pressure expansion tank or significant changes in hot water temperature may also cause surges in building water pressure: some building plumbing systems include an expansion tank on the water supply system, often on the hot water piping (details about these expansion tanks are
at WATER PRESSURE REDUCER / REGULATOR).
If the expansion tank suffers an internal failure such as a perforated bladder, the tank will stop functioning, will not protect the system from temporary increases in hot water pressure. Also
see HOT WATER PRESSURE EXPANSION RATE.
Water filter clogging: if your water system includes a cartridge-type water filter, typically installed to control or reduce sediment, debris, or odors, the filter may become clogged over time, resulting in a reduced water flow rate.
Some folks confuse water flow rate (how fast water comes out of the tap) with water pressure (static pressure when water is not being run). And lots of people call our water flow rate "water pressure" which it is, in a practical sense - the pressure with which water comes out of the tap.
Variation in performance of the pressure regulator itself: a water pressure regulator may be misbehaving.
One water pressure regulator failiure mode causes gradual increases in building water pressure above the set point on the regulator. This may be due to an internal failure or leak in the water pressure regulator, dirt on the regulator valve seat, or a leak in an internal regulator valveo pressure-sensing diaphraghm.
How do we Diagnose Poor Municipal Water Pressure & Flow in a Building - 5 Key Checks
Key things to check when water pressure and flow are inadequate in a building served by municipal water supply are
The condition of individual plumbing fixtures, faucets, valves, and controls. A clogged sink or shower strainer will cause bad water pressure at individual fixtures while others may flow freely. A plumbing shutoff valve that is partly closed or clogged with debris will cause bad water flow at that fixture.
The incoming municipal supply pressure. The municipal water supply source may be delivering water at low pressure.
The condition of water piping between the building and the street water main. An older water supply pipe connecting the building to the water main in the street may be small in diameter, clogged with minerals, rust, or debris, or it could be leaking underground.
The condition of building water supply piping. Clogged pipes due to minerals or rust, small diameter piping, long piping
The setting of the water pressure regulator at the building water meter or water shutoff valve. This topic is discussed just below.
Bad water pressure regulator or bad pressure regulator adjustment: (poor municipal water pressure) if the building is connected to a municipal water supply there may be a water pressure regulator installed, usually close to the water meter or where the water supply pipe enters the building.
If the water pressure control was set too low to start with or if there is a problem with the water pressure regulator, you may see an improvement in water pressure by diagnosing and adjusting or repairing this control.
If the loss of water pressure was sudden, it's not likely to be a problem the pressure regulator except in the less common cases of a blockage or failure in the regulator itself.
In this photo our flashlight lights up a (rather amateurish looking) water pressure regulator installed on a municipal water supply.
You can see that a previous connection to the water meter was cut, left shut off (see that shutoff valve at the left hand vertical pipe - what happens
if someone opens that valve?), and new fittings were installed to conduct incoming water to the building water supply piping.
The use of smaller
diameter flexible copper tubing might restrict the incoming water flow, but the presence of a pressure regulator at all suggests that the incoming
pressure may have been excessive. (Too high water pressure leads to fixture leaks.)
How to Adjust the Water Pressure Regulator on Municipal Water Supply
We have already mentioned checking and adjusting the pressure control for the water pump on a private
well system - just above. But what if the home does not have it's own well - what if the building is connected to a municipal water supply?
Watch out: don't set the water pressure reducing valve higher than necessary. Doing so wastes water and as we discuss
at WATER PRESSURE TOO HIGH: DANGERS, setting water pressure too high can cause both plumbing problems and actual serious safety hazards at buildings.
A Guide to Building Water Pressure by Adjusting or Repairing the Water Pump Pressure Control Switch on a Private Pump and Well Water Supply
For details about diagnosing poor well water pressure and flow, start
atWELL WATER PRESSURE DIAGNOSIS or go directly to the individual items listed just below.
How to Adjust Water Pump Pressure: The detailed, step by step procedure for inspecting and adjusting the water pressure control switch is
discussed in detail
at ADJUST PUMP PRESSURE CONTROL.
Diagnosing Water Pump Short Cycling on and off: If your water pump is clicking on and off too often or quite rapidly
see SHORT CYCLING.
Diagnosing Water Pressure Drops without explanation when the pump stops,
see WATER PRESSURE FALLS SLOWLY, ERRATIC PUMP: bad pressure control switch, building water running or leak, bad pressure gauge, bad check valve, bad foot valve.
Diagnosing & Repairing Lost Air in the Water Tank: The problem of lost air in the water pressure tank along with how to correct that condition are discussed
at SIGNS OF AIR LOSS.
Diagnosing & Repairing a Water Pressure Control or Water Pump Control Switch: We discuss diagnosing and repairing a water pressure control switch that sticks "on" or "off" or simply won't operate, at WATER PUMP PRESSURE SWITCH REPAIRS
Question: water pressure in the system varies too much
I have a water system based on a tank plus demand pump. The problem at the moment is that the pressure in the system varies too much between full pressure and the cut in of the demand pump. i.e. while taking a shower the water temperature drops markedly. What is the problem? - Anonymous by private email.
Then watch your pressure control and pressure gauge as water is running to see if the pump is turning on when the pressure falls to the pressure switch CUT-IN pressure setting. If not the switch is clogged or damaged and needs replacement. Do let me know what questions remain after that and I'll be glad to research and respond in detail. - Editor.
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Water pressure varies while taking a shower; sometimes the warm shower gets too cold
I get a noticeable water flow variation, especially during a shower. When the well pump kicks in it over powers the hot water significantly making a warm shower cold. Any ideas what I should do?
Reply: Regulating water temperature at the shower during normal pump operating cycles
If your hot water runs too cool when the water pump turns I suspect that your hot water piping or hot water source is clogged - perhaps if you are using a tankless coil that is mineral clogged this would be more likely. You could install an automatic mixing valve right at the shower - that valve is designed to keep water temperature constant; first try partly closing the individual cold water shutoff valve for your bathroom - by this I mean a valve in the cold water line that is "ahead" of or before the shower itself. By restricting the cold water flow rate in the piping you may improve the pressure balance.
But overall I suspect the problem is more likely to be clogging in the hot water piping or hot water supply system. That's because the PRESSURE produced by the pump is the same at both hot and cold water piping. It's the FLOW through piping systems that is more likely to vary. A similar effect is found when you're in the shower and someone flushes a toilet or turns on cold water at a nearby sink - and you are suddenly scalded.
It is normal for building water pressure to vary between 20-40 psi or 30-50 psi depending on how your pump pressure control switch is set. Even after you've de-clogged your hot water supply you can make a still better improvement in regulating water temperature at the shower by installing an anti-scald device or valve, either at the hot water source or right in the bathroom at the fixture.
Question: our water pressure comes on fast but quickly drops off to nothing. Is this a clogged pipe problem?
OMG my farm house was built before christ and my pressure gauge on my well has 60 psi works fine except I don't have any pressure in the house, I can turn on a faucet and it fast then drizzles down to nothing and if the kitchen sink is running there is next to none in bathroom, if filling washing machnine there is no water upstairs untill the washer fills up. takes at least 5-7 minutes for toilet to fill and 20 for the tub. How can I get the rust out of my pipes w/o tearing the house apart. I believe that they are clogged with rust since it is hard well water. - Lisa
Lisa if you have no actual water pressure but the gauge is reading showing pressure is present, and provided no one closed a water valve between tank and house, I suspect that the gauge pressure reading is wrong and the gauge is stuck. Try tapping on the pressure gauge to see if it moves.
The same crud that clogs the valve can clog the pressure sensing switch and interfere with proper well pump operation. If it's a rust and sediment problem your plumber might install a filter ahead of the rest of the water equipment.
Take a look at CLOGGED SUPPLY PIPING, but because the water pressure falls off quickly you'll also want to be sure that the water pressure tank is not waterlogged, causing the well pump to have to turn on and off too frequently. See WATER PUMP SHORT CYCLING to diagnose well pump short cycling and water pressure that rapidly rises and falls.
If on the other hand water pressure falls off and takes a long time to recover, I suspect that the well itself is running out of water. For that problem see WELL FLOW RATE and also how to measure the WELL FLOW RATE.
Thank you Mr. Friedman I will certainly try that with a light touch upon looking into the well I saw a capusule looking clear plastic part rustly what is that called and maybe that needs to be replaced I posted this alittle while ago and it didn't show up I turned all water off waited opened all faucets turn back on and no water b/c all faucets were open left only kitchen and water hardly any rust or air not like it use to when we hard power failure as no lights no water. Thank you for helping me, Lisa
Question: high water pressure, varying pressure, & burst components led to a leak
5/19/15 LB said:
All while back I had a problem with my water line bursting at my water meter. It happened on a day when the municipality had turned off the main water to all the rural area. When the water was turned back on, my line burst. I checked my water pressure at the meter and it is 102 PSI. Is that within a reasonable range? I also have a regulator in my home that was installed prior to me purchasing the property. From what I can gather, the previous owners had problems with seals and valves blowing, hence the regulator.
(May 20, 2014) Dale said:
I am on a municipal system with a pressure reducing valve in line. Most of the time the pressure gauge on the house plumbing lines would read 50-60 psi, however I had a problem with the water pressure creeping up to over 100 psi. Simply turning on the water for a few seconds would drop the pressure back down. Looking at the gauge later it could be normal or over 100 psi. I changed the pressure regulator with a new one and it's doing the same thing again. Any suggestions?
Indeed 102 psi is quite high and would be expected to give recurrent leaks at fixtures inside a building IF the building's water pressure regulator was not working or was not properly adjusted.
Watts corporation as well as other manufacturers produce a wide range of pressure reducing & regulating valves.
Usually a "direct acting" pressure regulator is what's installed in homes.
For high pressure commercial operations one might need to install a pilot-operated pressure regulator but in a private home that has very high incoming or widely varying water pressure it's more likely that a 2-stage pressure reduction that I will cite below is what's needed. Watts.com describes these products from which I paraphrase or adapt:
Direct acting valves, the more popular type of a water pressure reducing valves, consist of globe-type bodies with a spring-loaded, heat-resistant diaphragm connected to the outlet of the valve that acts upon a spring. This spring holds a pre-set tension on the valve seat installed with a pressure equalizing mechanism for precise water pressure control. - retrieved 5/19/15, reference source http://www.watts.com/pages/learnAbout/reducingValves.asp?catId=64
You certainly need a pressure reducing valve that can handle the pressure range your municipality delivers, which might mean installing two valves in series - a two-stage, "serial reduction" pressure reduction system. You don't
usually need two stages unless the incoming water pressure varies and is sometimes at 200 psi or higher.
In sum, I suspect the problem is that the original pressure reducing valve you had installed was either improperly selected, adjusted, or perhaps it just failed.
Question: poor shower pressure
(Oct 22, 2014) doug said:
i have a private well tyhat was installed in 1998, it has started recently having good pressure then dropping off almost to nothing then jumping back up. this just started
(Nov 10, 2014) Steve said:
My water pressure is low in the shower until I turn on another device. If I turn on one of the sinks in my bathroom the pressure in the shower goes up and back to how it used to be.
Any ideas? I have a fancy valve from Kohler but that was ruled out. I have 2 other heads in there and it acts the same even without the main. 2 plumbers can't figure it out...Help!
Russ I see a question from Steve - is Russ = Steve?
Low shower pressure: if that's the only fixture suffering - start by removing the shower head and checking the flow. If flow is good clean or replace the shower head. If flow is poor there is a blockage in the line to the shower or one of its valves.
When turning on another fixture improves water pressure I can but infer that the added flow turned on the pump.
12/1/2014 John Schult said:
Replaced pressure switch (40-60) Added 38psi air engaged new switch ran for 15 seconds then stopped. Waited 1 1/2 minutes re-engaged power did same thing will not run complete cycle. ?
Sounds as if the tank is water-logged or water is not able to enter the tank. Or the tank was simply nearly full. Try running some water in the building.
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"D'Arcy-Weisbach Equation for Pressure and Head Loss, used to calculate pressure or head loss due to friction in ducts, pipes, and tubes", Engineering Toolbox, web search 09/21/2010,original source
Watts, 815 Chestnut Street, North Andover, MA, USA 01845-6098, web search 09/18/2010 Watts Regulator Corporation, 815 Chestnut Street, North Andover, MA, USA 01845-6098, provides pressure and temperature relief valves, water pressure test gauges, water pressure regulators, backflow preventers, check valves, and other plumbing and heating controls and supplies. Website: http://www.watts.com/
Watts Backflow preventers - 978-688-1811
Watts Control valves - 713-943-0688 for example Watts pressure reducing valves, original source: http://www.watts.com/pages/learnAbout/reducingValves.asp?catId=64
Watts Drainage products - 828-288-2179
Watts Potable water PEX plumbing - 978-688-1811
Watts Water safety controls - 978-688-1811
Watts Water quality & conditioning products - 352-465-2000
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Typical Shallow Well One Line Jet Pump Installation, Grove Electric, G&G Electric & Plumbing, 1900 NE 78th St., Suite 101, Vancouver WA 98665 www.grovelectric.com - web search -7/15/2010 original source: http://www.groverelectric.com/howto/38_Typical%20Jet%20Pump%20Installation.pdf, [Copy on file as /water/Jet_Pump_Grove_Elect_Jet_Pumps.pdf ] -
Typical Deep Well Two Line Jet Pump Installation, Grove Electric, G&G Electric & Plumbing, 1900 NE 78th St., Suite 101, Vancouver WA 98665 www.grovelectric.com - web search -7/15/2010 original source: http://www.groverelectric.com/howto/38_Typical%20Jet%20Pump%20Installation.pdf, [Copy on file as /water/Jet_Pump_Grove_Elect.pdf ] - Cooperative Extension, School of Forest Resources, web search 07/24/2010, original source: http://pubs.cas.psu.edu/FreePubs/pdfs/XH0002.pdf
Water pressure tanks - how to diagnose the need for air, how to add air, stop water pump short cycling to avoid damage - water storage water pressure tank safety.
WATER PUMP REPAIR GUIDE an specific case offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost
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