The
Temperature/Pressure Relief Valve
One
of the most common code violations our inspectors
observe in the field involves the Temperature/Pressure
Relief (TPR) Valve on the water heater unit.
The purpose of this article is to assist
property owners and inspection professionals in
identifying these common code violations so they may
be prevented and corrected.
What
is a Temperature/Pressure Relief Valve?
Section
3303.1 of the International One- and Two-Family
Dwelling Code[i]
requires the installation of a combination Temperature/Pressure
Relief Valve (commonly referred to as a TPR valve)
or a separate temperature relief valve and a pressure
relief valve on every water heater. The purpose of the
TPR valve is to provide an important safety mechanism
that allows for the immediate discharge of excess
temperature and pressure that builds up inside the
tank as the water is heated.
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If
not allowed to properly discharge, this excess
temperature and pressure will eventually cause the
tank to explode.
One such tragedy occurred in Spencer, Oklahoma
at the Starr Elementary School on January 9, 1982
where six children and a teacher were killed when the
school’s water heater exploded with the force and
effect of two pounds of dynamite.
This occurred due to a malfunctioning TPR
valve. Figure
1 (right) shows a typical Temperature/Pressure Relief (TPR) Valve
installation on a gas water heater.
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Figure
1 - Typical installation of a
Temperature/Pressure Relief (TPR)
Valve on a gas water heater |
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Code Section 3303.3[i]
dictates that a TPR valve must discharge once the
pressure inside the tank reaches 150 psi (pounds per
square inch). Code
Section 3303.4[ii]
specifies that the TPR valve must be installed within
the top 6 inches of the water heater tank in order to
enable the valve to discharge at a temperature of no
greater than 210°F.
As a result, any discharge piping must be rated
to withstand at least 210°F to prevent melting and
blockage of the TPR valve when discharged. |
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Common
Violations in the Field
As
we have seen, the presence of a functioning
Temperature/Pressure Relief (TPR) Valve on a water
heater is extremely important.
However, there are other factors to consider in
ensuring the protection of property and people who may
be standing near the water heater when the valve
actually discharges. Namely, where does the scalding water or steam go once the
valve is allowed to discharge?
The
following are the more common discharge piping
violations we observe in the field:
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1)
Improperly-Sized Discharge Pipe
Code
Section 3303.6.1.[i]
requires that the TPR valve is fitted with a discharge
pipe that provides the same size opening as the
valve outlet itself. |
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2 (right) shows a TPR Valve that has been fitted with a discharge pipe that
is smaller than the size of the valve outlet.
This is a common defect that is strictly prohibited because smaller
discharge pipes restrict the flow of the pressurized water released by the valve. This creates a dangerous bottleneck,
building-up even more pressure at the point of discharge that can cause the
tank to explode.
Personal injury (or death) and property damage may result. |
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Figure 2 - Improperly
sized TPR discharge pipe |
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2)
Missing Discharge Pipe
In
many instances, the discharge pipe required in Section 3303.6.1.[i]
was never installed at all.
This normally occurs during replacement or initial installation of
the water heater. |
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Figure
3 (right), shows a missing TPR discharge pipe.
This creates a dangerous condition whereby the TPR valve will spray
scalding steam or scalding hot water onto anyone (or anything) that happens
to be near the water heater when discharge occurs.
When
you consider that the TPR valve discharges water at 210° F., serious injury
or property damage will result.
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Figure 3 - Missing TPR
Valve discharge pipe |
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3)
Improper Termination of the Discharge Pipe |
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Ideally,
the TPR valve discharge pipe will be vented to the outside of the building
where the scalding water or steam can be discharged without posing a threat
to people or property.
However, in many installations direct piping to the outside is not
possible or is deemed to be too costly to provide.
Accordingly,
Code Section 3303.6.1[i]
does allow for the discharge pipe to terminate inside a receptacle (or
spill pan) as long as an air gap is provided between the end
of the discharge pipe and the top rim of the spill pan itself without
creating a hazard or potential cause of damage. |
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This
is clearly not the case in Figure 4 (right). Here we see the copper
discharge pipe runs down the right hand side of the water heater tank to
terminate into a metal spill pan below.
However, the problem lies in the fact that the end of this discharge
pipe terminates below the upper rim of a shallow spill pan.
This
installation of the discharge pipe poses several potential dangers.
First,
the discharge pipe may be able to siphon any liquid that may accumulate
inside the pan. This is due to the fact that the end of the discharge pipe
terminates below the top rim of the receptacle itself. Once siphoning
occurs, the liquid (be it dirty water, household chemicals, oil, etc.) will
be drawn back into the water heater tank, thereby contaminating the
household drinking water supply. |
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Figure 4 - Improper
Termination of Discharge Pipe. |
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While
this occurrence is admittedly unlikely due to the fact that the TPR valve
would have to fail (stay open) while a simultaneous drop in line pressure
would create a siphon, the mechanical potential does exist for this
contamination to occur.
Thus the air gap provision in the building code.
Secondly,
and even more likely, is the risk of personal injury when this TPR valve
discharges.
This is because the discharge pipe terminates into a spill pan that
cannot safely catch the flow of water or steam during discharge.
When you consider that the TPR valve discharges at 150 psi, which is
five times greater than the force of your garden hose, the scalding water
can strike the bottom of the shallow pan and spray out in all directions.
Therefore,
a deeper spill pan receptacle with adequate circumference would be advisable
over the shallower, tightly-fitting spill pans commonly observed in the
field. |
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Figure
5 (right), shows a spill pan that tightly fits the base of a water
heater. Unfortunately, such an installation accomplishes little in the way
of catching water or steam from the TPR safety discharge valve, rendering
the spill pan useless.
Spill
pan installations depicted in this photograph are common in condominiums and
some residential homes where space is a premium. |
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Figure
5 - Inadequate Water Heater Spill Pan Sizing |
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Summary
As
we have seen, the Temperature/Pressure Relief (TPR) Valve serves an
extremely important function – ensuring the safe and proper operation of
the water heater.
As professional home and commercial property inspectors, we
frequently observe the code violations discussed in this article and
encourage property owners and inspection professionals to take the time and
effort to identify and correct them.
Consequently,
the conditions presented in this article should be corrected immediately by
a qualified and licensed contractor. |
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Please
Contact Us
If
you have any questions, comments or suggestions regarding the information
presented in this article, or if you would like to schedule an inspection of
your property to identify these and other common property defects, please
feel free to contact us directly:
Guardian
Inspection & Information Services |
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E-mail
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info@myguardian.com
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World Wide Web
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www.myguardian.com
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Telephone
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321.639.2743
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Facsimile
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321.636.6377
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Address
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Guardian Inspection & Information Servicesā
113 Tropic Place
Rockledge, FL 32955 |
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End Notes |
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[1]
International One- and Two-Family Dwelling Code™ 1998, Copyright © 2000
by International Code Council, Inc. Published in cooperation with: Building
Officials and Code Administrators International, Inc., International
conference of Building Officials and Southern Building Code Congress
International, Inc., Incorporated the provisions of the 1995 edition of the
CABO One and Two Family Dwelling Code Promulgated by the council of American
Building Officials (CABO).
NOTICE: The
information presented in this article is intended for educational purposes
only. It is not intended to
identify or predict all the potential defects or conditions that may exist
and be considered for a complete analysis of a given property.
End
of Article
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