pressure relief valves be mounted horizontally?
Although valves can be physically mounted horizontally, they are designed to
be mounted with the stems in the vertical position. Mounting the valve in other
than the upright vertical position can lead to poor valve performance with
excessive seat leakage.
much seat leakage can I expect from a pressure relief valve?
Pressure relief valves come in a variety of seat configurations. In normal
operation, most valves with metal to metal seats are allowed a certain amount
of leakage past the seats. American Petroleum Institute Standard 527, Seat
Tightness of Pressure Relief Valves defines the most widely used method for
testing seat tightness as well as the leakage rates. The rates are defined
by pressure category and valve size and range from 20 to 100 bubbles per minute.
The tests are conducted at 90 % of set pressure. Some valves like our 2600
and 2700 series can be supplied with optional "O" ring seats which
allow for zero leakage at 90 % of set pressure. The 3800 Series pilot operated
valve is supplied as standard with "O" ring seats and can safely
handle operating pressures up to 90 % of set pressure with no leakage.
often should a pressure relief valve be serviced?
The service and inspection interval for a pressure relief
valve will vary depending on the installation, service conditions
and type of valve in use. Each valve in a plant should be placed
on a specific service schedule based on the users operating
experience for each valve in a give application. Valves in
corrosive applications will require a shorter maintenance interval
than valves used on clean services. Other conditions that may
effect the service interval are low differential between operating
and set pressure, frequent valve operation, and excessive system
vibration. American Petroleum Institute Standard 576, Inspection
of Pressure-Relieving Devices can provide additional guidance.
are the benefits of soft seat valves versus metal seat designs?
Pressure relief valves with soft seats offer the benefit
of zero seat leakage when compared to valves with metal seats.
A typical metal seat valve is allowed to leak a certain amount
based on American Petroleum Institute Standard 527, Seat tightness
of Pressure Relief Valves. Valves with "O" ring seats
also offer the benefit of simpler maintenance by eliminating
the necessity of lapping the seat and disc as replacement of
the "O" ring and a light cleaning of the nozzle may
be all that is necessary. Valves with "O" ring seats
do have limitations based on the temperature range of the elastomer
that is selected and the users' ability to find a compound
that is compatible with the service fluid. Most "O" ring
valves are limited to a maximum temperature of 450 F depending
on the material selected. All Farris valves are available with
an optional "O" ring seat in a variety of materials
including Viton, Buna N, ethylene propylene, silicone and Kalrez.
When must I specify a lifting lever on a
Pressure Relief Valve?
Section VIII of the ASME Code covering pressure vessels requires pressure relief
valves to have lifting levers on air, steam, and hot water (over 140 F) service.
There are however instances where this requirement may be ignored. ASME Code
case #2203 allows for lifting levers to be ignored provided the following conditions
- The user has a documented procedure and
an associated implementation program for the periodic removal
of the relief valve for inspection, testing, and repair.
- The user specifies that no test lever be
- The user shall obtain permission to omit
the lifting lever (device) from the authority having jurisdiction
installation of pressure vessel.
These rules apply to valves installed in
ASME Section VIII applications. All valves used in ASME Section
I (Boiler) applications
require lifting levers except for those valves used in organic
fluid vaporizer service.
When must I specify
the use of a Balanced Bellows pressure relief valve?
Balanced bellows as used in our 2600 Series BalanSeal design are generally
specified for a variety of reasons. The most prominent is to nullify the effects
of back pressure in the discharge system on the valves set pressure. They are
also used to protect the principal guiding surfaces, spring, and valve top
works from coming in contact with a corrosive fluid. This may allow for the
use of less expensive metallurgy as the bellows isolates the trim from the
fluid. A balanced bellows valve should always be used when the variation in
back pressure exceeds 10 % of set pressure.
When should I specify a pilot operated relief
Unlike spring loaded valves that use a spring to hold the seat closed, pilot
operated valves use the system pressure to provide closing force. The Farris
3800 series pilot operated valve consists of a main valve that is controlled
by the all stainless steel PCF3 pilot control. Pilot operated valves offer
the advantage of actually becoming tighter as the operating pressure approaches
the set pressure. In addition, they are typically offered with soft seats that
allow for zero seat leakage up to 90 % of set pressures. Pilot operated valves
such as the 3800 series are normally used where maximum seat tightness is required
and where the operating pressure is close to set pressure. Generally they are
limited to operating temperatures of 450 F as they use elastomeric seats and
seals. In addition, care should be used on dirty services as pilot operated
valves are more prone to fouling than spring loaded types.