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This article describes how to select and use an air or water pressure gauge to obtain accurate pressure readings, and what causes inaccurate water tank pressure gauge readings. We explain how water gauges may become stuck or inaccurate and we suggest ways to test and repair misbehaving water pressure gauges. © Copyright 2012 InspectAPedia.com, All Rights Reserved. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website. How to Read Water Tank Pressure or any Pressure Gauge AccuratelyReaders should also see WATER TANK PRESSURE GAUGE where we describe water pressure gauges and their repair or replacement. Readers concerned with water pumps, tanks, and wells themselves should see WATER PUMPS, TANKS, TESTS, WELLS, REPAIRS. The page top photo shows the author testing the air pressure in a Well-X-Trol bladder type well tank. To buy or make your own portable water pressure measurement gauge, see WATER PRESSURE & FLOW MEASUREMENT.
Stuck Water Pressure GaugesFor digital pressure gauges such as the one we demonstrate in photos on This article , gauge accuracy and our ability to read the pressure gauge accurately may not be a concern. Our photo at above left shows the water pressure gauge at the bottom of a water tank. The left hand pressure gauge is "stuck" at a high pressure, probably from rust or debris entering the gauge bottom port. Our photo at above right shows an identical gauge (same manufacturer) installed on the same water system, but located on the water pump itself. It is reading accurately.
But for dial-type pressure gauges or for "stick type" tire gauges (photos above left and right) use an indexed stick that protrudes from the gauge bottom. The accuracy with which a gauge reports and you can read pressure varies. We don't trust stick-type pressure gauges for accuracy. Dirt on the sliding indicator gauge, age, loss of lubricant, quality of manufacture (on some units, not all), and errors in reading the gauge all lead to errors, sometimes substantial errors. Choose a Pressure Gauge With the Proper Operating Pressure Range
Diagnose Jumpy or Erratic Water Pressure Gauge ReadingsQuestion:I have an additional observation with regards to my well water system. I noticed last weekend when I was filling an above ground pool that the gauge at the well water pump was going as high as 20psi and then bouncing down to 0psi and then back to 20psi. The gauge was very jumpy. Is it possible that the well pump, although the well pump sounds like it is pumping properly, could possibly be flawed? The pressure tank was recently replaced due to a ruptured bladder. I have no Idea how long it was working that way for I purchased the house in October of 2009. I still believe that I have a pressure problem. I filled a pool so I do not think I have a water quantity problem. Could you please advice as to your thoughts on this issue? - Thanks, Tony Reply:Water pressure gauges can be jumpy due to a partly clogged gauge or gauge piping, defective gauge. A pump cycling on and off would not explain pressure reading varying between 0 and 20 unless your pressure gauge was not turning on the pump until pressure reached 0 - that'd be unusual. If you check water pressure and flow independently from the jumpy gauge you'll know what's going on and can then home in on the gauge if that's the problem. See the suggestions below for checking on the actual water pressure in a plumbing system and on comparing the system pressure and pump behavior to the gauge behavior. Other causes of odd pressure gauge behavior include an intermittent blockage at a water pressure tank such as a sticking water or air bladder. But a problem in the well, pump, tank, piping that is causing a pressure variation or fluctuation would be expected to also affect the pump pressure control switch and turn the pump on and off accordingly. So it's reasonable, from your description to check on the system pressure independently of the jumpy water pressure gauge. Ways to Check Water Pressure, Pump Pressure Controls, Water Pump Operation Against Gauge PressureUse an independent air pressure gauge or water pressure gauge and measure water pressure at
Try replacing the questionable water pressure gauge with a new one. Be sure that the mounting pipe or orifice where the gauge is installed is not blocked with sediment or debris. Check Water Tank Pressure Using an Independent Pressure GaugeOur photos just below show the author using a digital tire pressure gauge to measure the air pressure in a bladder-type water pressure tank or well tank.
Check the air pressure in the water tank by using an accurate air pressure gauge (such as a dial type or digital tire pressure gauge) to measure the air pressure at the schrader valve on the water tank. The tank pressure should be within 10% of the original factory water tank pressure setting. Our photo (above left) shows the water tank air inlet valve on the top of our Well-X-Trol well tank. We removed the cap and label for the photo. Our photos, below, show these same pressure gauges in use to measure air pressure in an automobile tire - a Mini Cooper run-flat tire that needs to be kept accurately at the proper air pressure. Be sure to press the gauge orifice down firmly and straight onto the air valve. Regardless of whether you are checking pressure in a vehicle tire or a home water system well tank, holding the gauge askew will cause air to be lost out of the pressurized container.
Causes of False Water Tank Pressure Gauge Readings - too high or too lowWhile normally water pressure gauges do a great job and are reasonably accurate, on a water tank a water pressure gauge can give very inaccurate pressure readings, especially if it's pressure intake port, a small diameter hole, or the small pipe on which it's mounted are debris clogged. If your water supply contains sediment or debris, or if the water is high in iron or mineral content, this blockage becomes more likely. False High Water Pressure IndicationsWater under pressure has entered the gauge at the high-end of the pump on cycle, but its exit is blocked or slowed by blocking debris at the gauge. So when actual water system pressure falls (water is drawn out of the system, pressure drops typically 20 psi before the pressure switch turns the pump back on), the gauge continues to read higher than actual pressure. False Low Water Pressure IndicationsThe system water pressure has fallen, perhaps to just below the pump cut-in pressure, and stays there long enough for the pressure gauge to slowly bleed its own higher pressure water out through a partly blocked opening. The indicated pressure on the gauge falls to some low level, in some cases even near zero. Additional water is drawn from the system, the pressure drops just enough more that the pressure control switch turns on the pump and system water pressure rises up to the cut-off or cut-out water pressure. But the gauge continues to read a false "low" because incoming water to its sensor port is blocked by debris. Note that these debris blockage conditions that cause false high or low water pressure indications on a water pressure gauge are the same conditions that can occur at a water pump pressure switch, causing it to misbehave as well. A water pressure gauge can also indicate incorrect pressure simply because the gauge is inaccurate (this is not precisely calibrated lab-grade equipment) or because the gauge has become damaged. Remedy - How to Correct A Water Pressure Gauge that Reads too High or Too LowThe well pump is turned off, pressure is drained from the system (you do not have to let all of the water out of the tank, just be prepared for a little spillage). Then the new water pressure gauge is prepared for installation (make sure the gauge bottom threads match those of the old unit being replaced as diameters vary from 1/4" to 1/2"). See WATER TANK PRESSURE GAUGE for details of how to repair or replace a water tank pressure gauge. Frequently Asked Questions (FAQs) about the precision and accuracy of water pressure gauges and what causes water pressure gauges to read incorrectly or get stuck... Ask a Question or Search InspectApediaQuestions & answers or comments about water pressure gauges and pressure gauge accuracy. Ask a Question or Enter Search Terms in the InspectApedia search box just below. Technical Reviewers & ReferencesRelated Topics, found near the top of this page suggest articles closely related to this one.
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