Water pressure too high:
This article describes the dangers of excessive water pressure in buildings: safety hazards include burst water tanks or boilers, clogged relief valves, and even building flooding and mold contamination.
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As we explain in more detail at WATER PRESSURE REDUCER / REGULATOR, often municipal water supply pressure can run quite high, say over 80 psi and in some communities, more than 150 psi.
Some national and regional plumbing codes require that the maximum static water pressure should be not more than 80 psi (5.5 bar).
Watts Corporation and other plumbing manufacturers recommend that a water pressure regulator should be installed in buildings where water pressure exceeds 60 psi. T
here are good reasons for this upper limit on building water pressure, as we list here.
To accurately determine the water pressure in a building using a simple water pressure test gauge, see WATER FLOW RATE MEASUREMENT.
Our sketch above, courtesy of Carson Dunlop, shows the key components found where a municipal water supply enters a building.
Watch out: although normal municipal water pressure is under 70 psi, when the building's pressure reducing valve is set too high even if a water heater is protected by a thermal expansion bypass valve, that safety device may become ineffective due to the high inlet water pressure.
This combination of circumstances can produce high inlet water pressure at a water heater tank that combines with thermal expansion pressure to create unsafe water pressures in the system. If we add to this list of water heater overpressure risks the chance that an upper-limit temperature control is damaged or tampered-with, severe overheating at a water heater tank and even a BLEVE explosion can can occur.
Watch out: BLEVE explosions or boiling liquid vapor explosions can occur at both domestic water heaters (calorifiers or geysers) and at hot water heating boilers (hydronic heating systems). We discuss the role of pressure/temperature relief valves in protecting against these hazards
at RELIEF VALVE, TP VALVE, BOILER
As we further explain
at RELIEF VALVE, WATER HEATER, in some locations where hard water is found, an expansion control valve is also used to drain excess hot water tank pressure.
If the building water pressure gauge reading is ever found at 80 psi or higher, you will want to install a water pressure regulator at the point where water supply enters the building. Watts produces a Watts Governor 80™ used for this purpose, but other manufacturers also produce a wide variety of water pressure regulators. If your building already has a water pressure gauge installed, it may be defective or it may be set too high.
At HOT WATER PRESSURE EXPANSION RATE we discuss how we measure water pressure and how temperature changes affect water pressure in a closed water heater tank or heating boiler.
And as we discuss
at WATER PRESSURE REDUCER / REGULATOR, too-high incoming water pressure at a building can cause both dangerous conditions (bursting water tanks, heaters, boilers, piping, lime-clogged relief valves), and costly building flooding and mold contamination. That article also describes solutions to high incoming water pressure.
Watch out: If the building water pressure gauge reading is ever found at 80 psi or higher, you will want to install a water pressure regulator at the point where water supply enters the building.
Watts produces a Watts Governor 80™ used for this purpose, but other manufacturers also produce a wide variety of water pressure regulators. If your building already has a water pressure gauge installed, it may be defective or it may be set too high
If your static water pressure is too high on a municipal supply, you should adjust the water pressure regulator. A link to that procedure is given below at MORE READING
The articles listed just below discuss how water pressure reducers / pressure regulators work and how to adjust a water pressure regulator:
Watch out: If your well water pressure is too high, the system may be unsafe.
"Wire draw" problems occur in a diaphragm-type (residential) pressure reducing valve at low or intermittent water flow rates that happen to be close to the shut-off or "close" point of the pressure reducer, the valve mechanism becomes unstable and begins to "hunt" for the proper valve seat position.
You'll notice wire draw on a pressure reducer valve if you hear chattering or noise caused by this rapid cycling, almost vibration, at the valve seat at low water flow conditions.
The underlying cause of wire draw problems on pressure reducing or pressure regulating valves occurs because the valve, probably the wrong model for where it is being used, is forced to operate for long periods at low flow rates very close to the "close" position of the pressure regulating valve. Water flowing over the valve seat through this nearly-closed very small opening can wear a groove or depression in the seat.
As a result, water may flow through that little opening even when the valve has closed. The continued flow of water through this worn groove or depression continues to form and enlarge this "wire-shaped" slot in the pressure reducing valve seat.
What happens when a pressure reducing valve is suffering from wire draw? When no plumbing fixtures are being operated in the building for a period of time, water pressure will slowly increase above the intended or regulated pressure. The result, if we're lucky, is a mysterious leakage from pressure relief valves such as found on water heaters or boilers in the building. In the worst case, an overpressure condition at a water heater or boiler might damage the equipment or even render it unsafe.
Watch out: For example, chronic leaks out of a pressure/temperature relief valve, combined with a water supply high in mineral content, can lead to eventual pressure-temperature valve clogging and failure to operate in an emergency overpressure or overheating condition, resulting in
a BLEVE explosion or boiling liquid vapor explosion. Or less dramatic, building leaks that cause flooding can also lead to costly mold contamination.
Watts discusses the wire draw problem in their literature on water pressure reducing valves. Watts points out that selecting a pressure reducer control that is properly-sized for the building and the incoming water pressure will avoid wire-draw and the potentially catastrophic failures to which wire draw can lead. A smaller pressure reducer valve or a pressure reducer with a stainless steel valve seat to resist corrosion is likely to be better in this case.
Watts informs us that:
In general, the minimum flow through a water pressure reducing valve should be 10% to 15% of the maximum flow rate desired in the system. Also, water pressure reducing valves should be selected based on the flow and pressure ranges listed in the literature, not the size of the pipe to which they will be attached. You should select a regulator whose operating pressures fall within the middle of its rated range.
WATER PRESSURE REGULATOR ADJUSTMENT explains how to adjust this device.
Continue reading at WATER PRESSURE MEASUREMENT or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see WATER TANK SAFETY
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(June 24, 2011) Anonymous said:
Is there a maximum pressure that cities can deliver water to a home?
(July 8, 2011) (mod) said:
There are recommended water pressure upper limits for within buildings, lest we have leaky faucets or worse. But municipal water pressure is permitted to be and in fact actually may be much higher in some areas. That's why we install a water pressure regulator at the point of water service entry into the building. The pressure regulator can protect the building from excessive municipal water main water pressures.
Pressures over about 70 psi invite leaks.
(Sept 2, 2012) Carla said:
My hot water heater is leaking and the pressure valve is acting erratic, the needle is moving really fast sometimes and right now the needle is at 160. What should I do?
Watch out: you are describing a dangerous condition risking a very serious, even fatal explosion of your water heater tank.
Shut the system off and ask for help from a licensed plumber.
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