12
4
Hydronic piping
Relief Valves
WARNING
For protection against excessive pressure,
install temperature and pressure protective
equipment required by local codes. A relief
valve must be certified by a nationally
recognized testing laboratory that maintains
periodic inspection of listed equipment or
materials. The equipment and materials
must meet the requirements for Relief Valves
and Automatic Gas Shutoff Devices for Hot
Water Supply Systems, ANSI Z21.22, as well
as the standard CAN1-4.4, Temperature,
Pressure, Temperature and Pressure Relief
Valves and Vacuum Relief Valves. The relief
valve shall be marked with a maximum
set pressure, not to exceed the maximum
working pressure of the appliance. It shall
also have an hourly rated discharge capacity
not less than the Btu output of the heat
source.
Pressure only relief valves (POV)
A pressure relief valve should be installed in the connection
provided on the top of the tank containing hydronic water. It
is imperative that the relief valve be correctly installed because
it also serves as an air vent. Do Not place any valve between
the relief valve and the opening provided. To prevent water
damage, the discharge from the relief valve should be piped to
a suitable floor drain for disposal when relief occurs Do Not
install reducing coupling or other restrictions in the discharge
line. The discharge line should allow complete drainage of the
valve and line. The POV should be sized in accordance with the
maximum working pressure of the tanks, and the Btu output of
the backup heat source.
It is recommended to have a relief valve sized in accordance
with ASME Boiler and Pressure Vessel Code, Section IV
“Heating Boilers”. ASME states in Section VIII, Division 1,
paragraph UG-125 (a), “All pressure vessels within the scope of
this division, irrespective of size or pressure, shall be provided
with pressure relief devices in accordance with the requirements
of UG-125 through UG-137.”
Figure 4-1 Relief valve
Verify that the relief valve complies with
local codes. If the relief valve does not
comply with local codes, replace it with
one that does. Follow the installation
instructions in this section.
Do not place a valve between the relief valve
and the tank.
NOTICE
IMG00111
Standard Installation
Relief Valve Discharge Piping
Relief valve discharge piping
MUST
be:
- Made of material serviceable for a temperature of
250°F or greater
- Directed so that hot water flows away from all
persons
- Directed to a suitable place for disposal
- Installed so as to allow complete draining of the relief
valve and discharge line
- Terminated within 6" of the floor
Relief valve discharge piping
MUST NOT
be:
- Excessively long. Using more than two (2) elbows or
15 feet of piping can reduce discharge capacity
- Directly connected to a drain (Refer to local codes)
- Subject to freezing
WARNING
Do not install any valve between the relief
valve and its connection or on the relief
valve discharge piping. Improper placement
and piping of relief valve can cause severe
personal injury, death or substantial
property damage.
CAUTION
The relief valve is not intended for constant
duty, such as relief of pressure due to
repeated normal system expansion. Correct
this condition by installing a properly sized
expansion tank in a domestic water system.
Refer to the expansion tank manufacturer’s
installation instructions for proper sizing.
WARNING
Failure to install and maintain a new, listed
and properly sized relief valve will relieve
the manufacturer from any claim which
might result from excessive temperature and
pressure.
Installation & Operation Manual
