DeLUX DP Operation Manual Download

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Smaller Relief Valves

The industry’s requirement for a small full-flow safety relief valve
challenged design engineers some years ago:

The valve must be leakproof before operating and must

reseat leakproof each time after each operation. The only
known satisfactory seat disc materials to accomplish this
have been special synthetic rubber compounds.

Valve discharge settings are relatively high and require

high spring loads to keep the valve closed.

Because of the small interior diameter of the valve, the

round metal seating area is small.

Safety Information - Relief Valves Don’t Last Forever

Debris on valve seats which prevents reseating can occur
whenever the valve collects material in the relief valve opening
which is not blown out when the relief valve opens.

Inspection of Relief Valves

Unfortunately many of the above problems may not be easily
observed because of the compact nature of some relief valve
designs.

A casual visual inspection of a relief valve may not necessarily disclose
a potential hazard. On the other hand, a visual inspection will often
disclose leakage, corrosion, damage, plugging and contamination.

If additional light is required, a flashlight should be used.

If there is any doubt about the condition of the valve, or if there is a
suspicion that the valve has not been protected by a cap for some
time, it should be replaced before refilling the container.

Eye protection must be used when examining relief valves under
pressure.

All of these parameters may result in the development of a
significant indentation in the rubber seat disc after some years.
The seat disc may have a tendency to cling to the metal seat. This
may result in the relief valve not opening at the set pressure as the
seat disc ages.

Test have been conducted on small LP-Gas relief valves of all the
U.S. valve manufacturers. Valves over 10 years old were removed
from service and tested to determine at what pressure the valves
discharged. In many of the valves, the pressure required to open
the valve exceeded the set pressure.

Because of the critical importance of proper functioning of relief valves,
common sense and basic safety practice dictate that small relief
valves should be replaced in about 10 years.

Some larger relief valves on bulk storage tanks can be replaced
with rebuilt valves obtained from the manufacturers. Small relief
valves cannot be rebuilt economically, thus, new valves are
required. Most LP-Gas dealers find it impractical and costly to test
relief valves and field repairing of relief valves is not sanctioned by
the manufacturers, Underwriter’s Laboratories, or ASME.

Use of Protective Caps

Many of the problems that cause inoperative relief valves could be
prevented if proper protective caps were kept in place at all times.

Collection of debris would be prevented. Contamination caused by
corrosive atmospheres would be reduced. Water collection in the
valves would be eliminated. Relief valves protected with caps
from the time of installation in the container would obviously have
a much longer safe useful life, but they still should be replaced at
some time because of the gradual deterioration of the rubber seat
disc due to age alone.

NFPA 58 requires that protective caps must be kept in place as
a protective cover on some relief valves. This is a mandatory
requirement on several types of relief valves. The fact that use of
caps may make inspection more time consuming should not be
viewed as a reason for either not using the caps, or not making
required periodic inspections.

In the event a relief valve has been used without the required
cap, the relief valve should be thoroughly inspected and the
required cap placed on the relief valve. If damage is noted to
the relief valve, it should be replaced and the replacement valve
should be capped. Relief valves with pipe-away adapters or
deflectors used on lift truck containers have been found choked
with debris. Inspection of relief valves with deflectors can only be
accomplished by removing the deflector.

Similarly, larger relief valves with vent stacks have been found
choked with debris and water. Valves have failed because springs
rusted through. The weep hole was plugged. It was obvious
that the relief valves had not been inspected in many years.
These conditions must be alleviated by periodic inspections and
replacement of relief valves as needed.

Summary Recommendations

Predicting the safe useful life of a relief valve is obviously not an
exact science. The conditions to which the valve is subjected
will vary widely and will largely control its life. In matters of this
kind, only basic guidelines can be suggested. The LP-Gas
dealer must observe and determine the safe useful life of relief
valves in his territory. The valve manufacturers can only make
recommendations for the continuing safety of the industry:

Make sure proper protective caps are in place at all times.

Do not release a container for service or fill a container
unless it has a protective cap in place.

Replace relief valves periodically, at least every 10 years.

Every relief valve has the month and year of manufacture
stamped on the valve. This is most particularly true of
small separate relief valves.

Carefully inspect valves each time before the container is

filled. Replace valves showing any signs of contamination,
corrosion, damage, plugging, leakage, or any other
problem. Eye protection must be used when examining
relief valves under pressure.

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