Pressure Relief Valves for Hot Water Heaters

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Questions and Answers

What type of safety relief valves are typically used in potable water heaters and hot water storage tanks?

Temperature relief valves (correct)

Pressure relief valves

Overflow and temperature relief valves

Overflow relief valves

What maximum pressure do the heaters and tanks operate at?

900 kPa

110 kPa

1200 kPa (correct)

1500 kPa

According to ASME BPVC IV, Part HLW-800.1, how many officially rated temperature and pressure safety relief valves should each water heater have?

At least two

At least three

At least one (correct)

At least four

What is the maximum allowable working pressure of the water heater according to ASME BPVC Section IV, Part HLW-800.1?

Less than the pressure setting of the relief valve Signup and view all the answers

What temperatures do the heaters and tanks not exceed according to the text?

99°C Signup and view all the answers

What is the purpose of using temperature and pressure safety relief valves in potable water heaters?

To prevent super-saturated hot water explosions Signup and view all the answers

What is the purpose of a combination temperature and pressure relief valve?

To provide protection for both overpressurization and dangerously high water temperatures Signup and view all the answers

How does the temperature sensitive element of a combination temperature and pressure relief valve work?

It consists of a wax-filled thermostatic sensor probe that extends into the water storage tank Signup and view all the answers

What is recommended for combination temperature and pressure relief valves?

Annual try lever tests Signup and view all the answers

What does a fusible element temperature relief device do?

Melts at 99°C and allows the hot water to escape, but does not reseat Signup and view all the answers

What happens when the water temperature rises to about 99°C in a hot water system with a temperature and pressure relief valve?

The temperature element opens, allowing the hot water to escape before becoming a supersaturated liquid Signup and view all the answers

What is the purpose of a safety relief valve on hot water heaters or tanks?

To relieve excess pressure only Signup and view all the answers

What is required if relief devices sensitive only to temperature are installed on hot water heaters or tanks?

Additional overpressure protection in the form of either a safety relief valve or a temperature and pressure relief valve must be provided Signup and view all the answers

What type of pressure element opens to relieve excess pressure in a combination temperature and pressure relief valve?

A disc held shut against a seat by a compression spring Signup and view all the answers

What is the function of the safety relief valve?

To relieve excess pressure only Signup and view all the answers

How can relief devices sensitive only to temperature be made sufficient for vessel protection according to ASME?

Additional overpressure protection must be provided, in the form of either a safety relief valve or a temperature and pressure relief valve Signup and view all the answers

What type of device employs a fusible element which melts at 99°C, allowing hot water to escape from the system?

Fusible element temperature relief device Signup and view all the answers

What opens a device at 99°C and closes it at 71°C, allowing the hot water to escape from the system?

A rod and tube arrangement device Signup and view all the answers

Study Notes

Safety Relief Valves in Potable Water Heaters and Hot Water Storage Tanks

Combination temperature and pressure safety relief valves are typically used in potable water heaters and hot water storage tanks.
These heaters and tanks operate at a maximum pressure of 150 psig (pounds per square inch gauge).
According to ASME BPVC IV, Part HLW-800.1, each water heater should have at least one officially rated temperature and pressure safety relief valve.
The maximum allowable working pressure of the water heater is 150 psig according to ASME BPVC Section IV, Part HLW-800.1.
The heaters and tanks do not exceed temperatures of 99°C (210°F).

Purpose and Function of Safety Relief Valves

The purpose of using temperature and pressure safety relief valves is to prevent overheating and overpressure in potable water heaters and hot water storage tanks.
A combination temperature and pressure relief valve combines the functions of a temperature relief valve and a pressure relief valve.
The temperature sensitive element of a combination temperature and pressure relief valve opens to relieve excess pressure when the temperature reaches a certain level.

Temperature and Pressure Relief Valves

A fusible element temperature relief device melts at 99°C (210°F), allowing hot water to escape from the system.
When the water temperature rises to about 99°C in a hot water system with a temperature and pressure relief valve, the valve opens to relieve excess pressure.
The purpose of a safety relief valve on hot water heaters or tanks is to protect the vessel from excessive pressure and temperature.

Additional Requirements and Functions

If relief devices sensitive only to temperature are installed on hot water heaters or tanks, an additional pressure-relieving device is required.
In a combination temperature and pressure relief valve, a spring-loaded pressure element opens to relieve excess pressure.
The function of the safety relief valve is to prevent damage to the vessel and ensure safe operation.
To make relief devices sensitive only to temperature sufficient for vessel protection according to ASME, additional pressure-relieving devices are required.
A device employing a fusible element which melts at 99°C, allowing hot water to escape from the system, is a temperature relief valve.
A device that opens at 99°C and closes at 71°C, allowing hot water to escape from the system, is a temperature-sensitive relief valve.

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Description

Test your knowledge about the construction and operation of pressure relief valves for potable hot water heaters, designed according to ASME BPVC IV, Part HLW, and operating at specific pressures and temperatures.