16 Questions
What is the direction of the outlet when a safety relief valve is installed in a horizontal position?
Pointed down
What is the minimum size of piping or fitting used to mount a safety relief valve?
Nominal pipe size equal to the valve inlet
Where can safety relief valves not be connected?
All of the above
What type of relief devices are considered insufficient for vessel protection by ASME?
Temperature-sensitive devices
What is the primary function of the temperature element in a combination temperature and pressure relief valve?
To sense high water temperatures
What happens when the wax in the thermal element of a combination temperature and pressure relief valve expands?
The valve disc lifts off the seat
How often are try lever tests on T&P valves recommended?
Annually
What happens to a fusible element temperature relief device when it melts at 99°C?
It stays open until replaced
What is the maximum allowable working pressure for commercial and industrial potable water heaters and hot water storage tanks?
1100 kPa
What type of safety relief valves are typically used in potable water heaters and hot water storage tanks?
Temperature and pressure safety relief valves
According to ASME BPVC Section IV, Part HLW-800, what is the minimum number of safety relief valves required for a water heater?
One
What is the basis for determining the pressure setting of a safety relief valve in a hot water supply system?
The maximum allowable working pressure of the component with the lowest rating
Where should a safety relief valve be installed on a water heater, according to ASME BPVC Section IV, Part HLW-801?
At least 100 mm from the top of the shell
How should the spindles of a safety relief valve be installed, according to ASME BPVC Section IV, Part HLW-801?
Upright and vertical
What is the maximum length of interconnecting piping allowed for a safety relief valve, according to ASME BPVC Section IV, Part HLW-801?
100 mm
Why are temperature and pressure safety relief valves used in potable water heaters and hot water storage tanks?
To protect against explosion dangers associated with super-saturated hot water
Study Notes
Safety Relief Valves in Commercial and Industrial Potable Water Heaters
- Safety relief valves are installed on commercial and industrial potable water heaters and hot water storage tanks, designed according to ASME BPVC IV, Part HLW.
- These heaters and tanks operate at pressures not exceeding 1100 kPa and temperatures not exceeding 99°C.
- Safety relief valves protect against explosion dangers associated with super-saturated hot water.
Temperature and Pressure Safety Relief Valves
- Most potable water heaters and hot water storage tanks use temperature and pressure safety relief valves.
- These valves protect against both over-pressurization and high water temperatures.
- ASME BPVC Section IV, Part HLW-800 refers to safety relief valve requirements for industrial and commercial potable water heaters.
Installation Requirements
- Safety relief valves must be installed not lower than 100 mm from the top of the shell.
- Valves must be directly connected to the water heater or a fitting connected to the water heater.
- Spindles must be upright and vertical, with no horizontal connecting pipe.
- No piping or fitting used to mount the safety relief valve can be smaller than the valve inlet.
- Safety relief valves shall not be connected to an internal pipe or a cold water feed line.
Combination Temperature and Pressure Relief Valves
- These valves provide protection for both over-pressurization and high water temperatures.
- The pressure element opens to relieve excess pressure, usually caused by thermal expansion.
- The temperature element opens when the water temperature rises to about 99°C.
- Unlike safety relief valves, T&P valves do not operate with a pop action when over-pressurization occurs.
Temperature-Sensitive Element
- The temperature-sensitive element consists of a wax-filled thermostatic sensor probe that extends into the water storage tank.
- When exposed to high temperature, the wax expands, lifts the valve disc off its seat, and discharges the overheated water.
- When the temperature returns to a safe level, the wax contracts, and allows the spring to reseat the valve.
Testing and Maintenance
- It is recommended that T&P valves receive annual try lever tests.
- Various types of temperature relief devices can be used, but they must always have additional pressure relief.
This quiz covers the ASME guidelines for the installation and connection of safety relief valves in water heaters, including prohibited practices.
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