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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. Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman. List of Problems Caused by Excessive Water Pressure in a Building
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 and other plumbing manufacturers recommend that a water pressure regulator should be installed in buildings where water pressure exceeds 60 psi. There 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. If the building water pressure is too high, here are some problems that you may encounter
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 VALVES - TP Valves on Boilers and at RELIEF VALVES - Water Heaters. As we further explain at RELIEF VALVES - Water Heaters, 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. For a discussion of temperature and pressure relief safety devices also see RELIEF VALVES - TP Valves on Boilers and RELIEF VALVES - Water Heaters. 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. The articles listed at WATER PRESSURE REDUCER / REGULATOR explain how to adjust a water pressure regulator: 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, see WATER PRESSURE REDUCER / REGULATOR. 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, see WATER PUMP CONTROLS & SWITCHES and see WATER TANK SAFETY. What is Pressure Reducing Valve Wire Draw and Why is it a Problem?"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. Mysterious Temporary Over-Pressure Water Pressure in Buildings: BLEVE explosions, Building FloodsWhat 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 explosions 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:
WATER PRESSURE REGULATOR ADJUSTMENT explains how to adjust this device. Frequently Asked Questions (FAQs)... Ask a Question or Search InspectApediaQuestions & answers or comments about the problems caused by building water pressure that is too high; diagnosis & cure of excessive water pressure; safety hazards of high water pressure; . 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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