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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. Readers should also see WATER TANK PRESSURE GAUGE where we discuss 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.

© 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

How to Read Water Tank Pressure or any Pressure Gauge Accurately

For digital pressure gauges such as the one we demonstrate in photos on this page, 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.

Our 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 low

While 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 Indications

Water 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 Indications

The 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 Low

The 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.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

PLUMBING TOPICS
WATER PUMPS, TANKS, TESTS, WELLS, REPAIRS
WATER PRESSURE REGULATOR ADJUST
WATER PRESSURE REPAIR GUIDE & COSTS
WATER PRESSURE LOSS DIAGNOSIS GUIDE
WATER PRESSURE & FLOW MEASUREMENT
WATER PUMPS & WELL TANKS
WATER PUMP & TANK SAFETY
WATER PUMP CONTROLS & SWITCHES
  IDENTIFY WELL PUMP TANK COMPONENTS
  MAIN WATER SHUTOFF VALVE
  WATER PUMP ELECTRICAL SWITCHES
  WATER PUMP PRESSURE CONTROL
    WATER PUMP PRESSURE CONTROL ADJUSTMENT
    WATER PUMP PRESSURE CONTROL REPAIR
    WATER PUMP PRESSURE CONTROL REPLACE
  WATER PRESSURE REGULATOR ADJUST
  WATER PUMP RELAY SWITCH
  WATER TANK AIR VOLUME CONTROLS
  TANK AIR INLET VALVE
  TANK AIR VALVE REPAIRS
  WATER TANK PRESSURE GAUGE
  WATER PRESSURE GAUGE ACCURACY
  WATER TANK DRAIN VALVE
  WATER TANK RELIEF VALVE
  CHECK VALVES
  WATER FILTERS
WATER PUMP TYPES & LIFE EXPECTANCY
WATER PUMP SHORT CYCLING
WATER PUMP & WATER TANK REPAIRS
WATER PRESSURE REPAIR GUIDE & COSTS
WATER PRESSURE LOSS DIAGNOSIS GUIDE
WATER PUMP PRESSURE CONTROL ADJUSTMENT
WATER PUMP PRESSURE CONTROL REPAIR
WATER PUMP PRIMING PROCEDURE
WATER PUMP WONT STOP RUNNING
WATER SUPPLY & DRAIN PIPING
WATER TANK TYPES: WATER, OIL, EXPANSION, ALL
WATER TANK AIR, HOW TO ADD
WATER TANK LIFE EXPECTANCY
WATER TANK PRESSURE CALCULATIONS
WATER TANK REPAIRS
WATER TANK REPLACEMENT
WATER TANK SIZE & VOLUME
WATER TANKS HOW THEY WORK
WATER SOFTENERS
WATER TESTS, CONTAMINANTS, TREATMENT
WELLS CISTERNS & SPRINGS
WINTERIZE A BUILDING

If You Need Help Diagnosing a Loss in Water Pressure or Other Pump & Well Problems See These Guides

WATER PRESSURE LOSS DIAGNOSIS GUIDE
WATER PRESSURE & FLOW MEASUREMENT
  Water Pressure Intermittent
  No Water Pressure
  Well Tank relation to Water Pressure
  Shaking the Water Tank?
  Water Pressure Tank Problems
  Water Pressure Tank Diagnosis
  Water pressure Later Returns "on its own"
  Water pipe clog diagnosis
  Water pipe clog repair guide
  Making the "right" repair
  Typical Water Tank & Pump Price

• Thanks to Jeremy Houser who suggested that we needed to clarify the difference between bladder type and non-bladder type water tanks when discussing air charging and diagnosis of water tank repairs.
• Amtrol Extrol™ pressure control tanks, which they call well tanks, are described at the company's website at www.amtrol.com/extrol.htm and installation and operating instructions for these well tanks can be found at www.amtrol.com/pdf/9015A290revcWXT.pdf
• Well-X-Trol: Amtrol Extrol™ pressure control tanks used on hydronic heating and other systems such as models 35LBC, 50 LBC, 85 LBC, and 100LBC to 600 LBC also use a bottom bladder containing air - see amtrol.com/pdf/LBCSeriesEXTROL9017-095.pdf for details.
• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Thanks to readers Nancy and Eric for questioning water pump gauge inaccuracies 11/2/2009
• Wessels Company bladder replacement store was found at westank.com/bladder-tank-store.php on 5/22/2009. Wes sell refers to "shock and surge tanks" as ASME replaceable bladder type and pre-charged hydropneumatic tanks used for commercial, industrial, and well water systems.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
• Plumbing Diagnosis & Repair: Water supply, drainage, septic systems, water testing, water contamination, defective plumbing materials & products.
• Water pump and pressure tank repair diagnosis & cost an specific case offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost
• Water pressure tank failures & water pump short cycling diagnosis and repair
• Cheating on water tests: Testing Water for Real Estate Transactions - make sure your water test is valid
• Drinking Water Testing Advice for home buyers home owners home inspectors
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