Sapag Safety Valves Series 8400/8500/8490/8590
Installation and Maintenance Instructions
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7. Style Variations
The Sapag Style 8400 pressure relief valve was designed with flexibility and interchangeability
in mind. Retrofitting from conventional to balanced bellows high performance liquid trim or soft
seat design is accomplished with a minimum number of new parts. These style retrofits can be
accomplished at lowest possible cost.
• Balanced Bellows
A Sapag 8400 conventional non-bellows pressure relief valve may be converted to a Style 8490
balanced bellows valve simply by adding the bellows assembly and tailpiece gasket.
• 8500/8590 Liquid Trim
Sapag Style 8400/8490 pressure relief valves in D to N orifice sizes may be converted to high
performance 8500/8590 liquid service design simply by replacing the standard disc holder with a
8500/8590 disc holder, or vice versa. For P to T orifice sizes a new nozzle ring is also required.
• O-Ring Soft Seat Design
Sapag Series 8000 pressure relief valves in all orifice sizes may be converted from the standard
metal-to-metal seats to an exceptionally tight soft seat design. This style conversion can be
accomplished by replacing the standard disc insert and nozzle with parts adapted to accommodate
the soft seat design.
The Sapag soft seat design uses standard size O-rings and is capable of handling pressures to
1480 PSIG. Standard O-ring materials include Buna N, EPR, Viton, Kalrez, Silicone and Teflon. (See
Figure 14 and Table 10).
8. Service Records
Service records should be completed before a valve is returned to service. These records are
important and will provide guidance on establishing time intervals between repairs as well as
providing the historical record of repairs and service conditions. Well kept records will be useful
in predicting when to retire a valve and which spare parts should be maintained in inventory to
ensure uninterrupted plant operation.
9. Spare Parts
When ordering spare parts, the valve serial number should be given together with set pressure,
part name and item number, valve size and style. On the valve nameplate the valve serial number
is shown.
Spare parts may be ordered from any Emerson Valves & Controls Regional Sales Office or
Representative.
10. Trouble Shooting Pressure Relief Valves
Troubles encountered with pressure relief valves can vitally affect the life and performance of the
valve and must be corrected at the first possible opportunity.
Failure of a pressure relief valve to function properly could result in the rupture of a line or vessel
jeopardizing the safety of personnel and causing damage to property and equipment. Some of the
most common troubles and the recommended correction measures are discussed in the following
paragraphs.
Seat Leakage
Of all the problems encountered with pressure relief valves, seat leakage is the most common and
the most detrimental. A leaking valve allows fluids to circulate into the secondary pressure zone of
the valve where it can cause corrosion of the guide and valve spring.
When a leaking valve problem is not immediately addressed, the leakage itself will further
contribute to seat damage through erosion (wire-drawing).
• Seats Damaged by Foreign Matter
Seating surfaces may be damaged when hard foreign particles such as mill scale, welding spatter,
coke and dirt are trapped between the seats. While this type of damage usually occurs while the
valve is in service, it may also happen in the maintenance shop.
Every precaution should be taken to clean the process system before installing a pressure relief
valve and to test the valve using only clean fluids.
Damaged seating surfaces are generally reconditioned by lapping. Most often small pits and
scratches may be removed by lapping alone. More extensive damage will also require remachining
prior to lapping.
In some instances valve construction can be changed to reduce the effects of seat leakage. The
use of an O-ring soft seat when applicable will minimize leakage and thus eliminate the associated
corrosion and erosion problems. If it is not possible to use a soft seated valve, or if the corrosive
media is present in the exhaust system, conversion to a Style 8490/8590 bellows seated valve will
isolate and protect the guides and valve spring from any corrosive fluids.
