Bulletin 71.4:1808
July 2010
Types 1808 and 1808A Pilot-Operated Relief Valves or Backpressure Regulators
W3716 |
W3507 |
Type 1808 |
Type 1808A |
Figure 1. Types 1808 and 1808A Pilot-Operated Relief Valves or Backpressure Regulators
Introduction
The Type 1808 globe-style and the Type 1808A angle-style, pilot-operated relief valves or backpressure regulators are economical, compact devices used in gas or liquid service to maintain pressure on oil and gas separators, and in pressure relief applications in gas distribution systems. The Types 1808 and 1808A are available with either a Type 6358 or 6358B pilot. The Type 6358 pilot is used in gas or liquid backpressure applications throughout the oil and gas production industry. This pilot offers a low bleed construction so
it only bleeds when it is repositioning the main valve. Pressure relief applications in the oil and gas industry are typically handled by the Type 6358B pilot. This pilot has a bleed restriction to reduce the buildup pressure required to reach wide-open flow. These units control pressures from 3 to 125 psig (0,21 to 8,6 bar), and the set pressure is varied to individual requirements by
the adjusting screw on the pilot. On gas service, the pilot exhaust can be piped into the downstream piping or vented to atmosphere. On liquid service, the pilot exhaust should be piped into the downstream piping or to a safe location.
Features
• Simple, Reliable Design—Units have fewer
parts for reliable service and minimum spare
parts inventory.
• Compact and Lightweight—Less than 12-inches
(305 mm) tall and weighs 25 pounds (11 kg) or
less, these units are easily transported and installed
where space is limited.
• Simplified, Convenient Installation in Any
Position—Pressure connection in diaphragm
casings and factory-piped pilot tubing mean
no upstream control line is required on standard
installations. There are no mounting restrictions to
limit service.
• Versatility in Both Liquid and Gas Service—
Pilot exhaust port and standard tapped pilot spring
case (Figure 2) both come with removable vent for
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remote piping when necessary. The standard |
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tapped pilot spring case comes complete with a |
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gasketed closing cap that permits pressure loading for |
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remote pneumatic adjustment of the set pressure. |
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D100163X012
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Bulletin 71.4:1808
Specifications
Available Configurations
See Table 1
Body Size and End Connection Style
2 NPT
Maximum Relief (Inlet) Pressure(1)
150 psig (10,3 bar) including buildup
Set Pressure Range
See Table 2
Differential Pressures Maximum: 125 psig (8,6 bar) Minimum: 5 psig (0,34 bar)
Type 6358 Pilot Bleed
Bleeds only when repositioning the main valve
Type 6358B Pilot Bleed
Continuously bleeds while inlet pressure is above set pressure
Flow and Sizing Coefficients
See Table 3
Main Valve Flow Capacities
See Tables 4 and 5 and Capacity Information section
Pressure Registration
Internal (standard) or External (optional)
Pilot Tubing and Connections
1/4 NPT with or without P590 Series filter
Temperature Capabilities(1)
-20° to 180°F (-29° to 82°C)
Construction Materials Main Valve
Type 1808 Body: Cast iron or WCC Steel
Type 1808A Body: Cast iron
Diaphram Plates and Diaphragm Casings:
Zinc-plated steel
Diaphragm: Neoprene (CR), Nitrile (NBR)
Construction Materials (continued)
O-Rings: Nitrile (NBR)
Gaskets: Nitrile (NBR)
Back-up Rings: Polytetrafluoroethylene (PTFE)
Spring: Zinc-plated steel (standard)
Valve Plug Guide: Stainless steel
6358 Series Pilots
Body: Aluminum or CF8M Stainless steel Spring Case: Aluminum or Stainless steel Body Plug: Aluminum or Stainless steel
Valve Plug: Nitrile (NBR) or thermoplastic plug with stainless steel stem
Spring: Zinc-plated steel
Diaphragm: Nitrile (NBR) or Fluorocarbon (FKM)
Spring Seat: Zinc-plated steel Stem Guide: Stainless steel Adjusting Screw: Zinc-plated steel
O-Rings: Nitrile (NBR) or Fluorocarbon (FKM)
Closing Cap: Plastic or Stainless steel Connector Cap: Stainless steel
Mounting Parts
Tubing: Stainless steel Fittings: Steel or Stainless steel Pipe Tees: Galvanized steel
Pipe Nipples: Malleable Iron, Galvanized Steel, and Stainless Steel
Options
• Upstream control line construction
• Pressure gauge (0 to 160 psig/0 to 11,0 bar/
0 to 1,1 MPa)
• P590 Series Pilot Supply Filter
Approximate Weights
Type 1808: 22 pounds (10 kg) Type 1808A: 25 pounds (11 kg)
1. The pressure or temperature limits in this Bulletin and any applicable standard or code limitations should not be exceeded.
• Quick Disassembly—With the removal of just two
nuts, the upper and lower casings lift away, exposing the trim and leaving the main valve body in the line.
• Optional Upstream Registration for Reduced
Buildup—For gas service with the Type 6358B
pilot, upstream control line construction is available
to provide wide-open relief flow capacity with less
buildup regardless of set pressure.
• Self-Draining Body—The Type 1808A angle-body
design has increased capacity and provides
complete process fluid drainage from body cavity during shut-down period or before disassembly of
the main valve.
Specifications
The Specifications section gives some general specifications for the 1808 Series Pilot-Operated Relief Valves or Backpressure Regulators. The nameplates give detailed information for a particular regulator as it comes from the factory.
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Bulletin 71.4:1808 |
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upper portion |
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upper portion |
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of valve plug |
diaphragm |
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of valve plug |
diaphragm |
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to exhaust |
assembly |
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to exhaust |
assembly |
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port |
hollow |
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port |
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lower portion |
passage |
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hollow |
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in valve |
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lower portion |
of valve plug |
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passage |
plug stem |
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of valve plug |
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in valve |
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plug stem |
to main valve |
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to main valve |
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diaphragm |
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diaphragm |
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FIXED RESTRICTION |
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restriction plug |
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TYPE 6358 BACKPRESSURE SERVICE |
TYPE 6358B RELIEF SERVICE |
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pilot exhaust |
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pilot
control spring |
spring |
diaphragm
valve plug |
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INLET PRESSURE |
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atmospheric pressure |
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Outlet/exhaust Pressure |
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loading pressure |
main valve |
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E0075 |
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Figure 2. Type 1808 with 6358 Series Operational Schematic
Principle of Operation
Refer to Figure 2. A pressure relief valve is a control device that opens to relieve fluid to atmosphere during an overpressure occurrence. A backpressure regulator is a control device that maintains a constant upstream pressure throughout a given flow range. It functions the same as a relief valve in that it opens on increasing upstream pressure. The Type 1808 or 1808A cannot be used as an ASME safety relief valve.
Pilots
A 6358 Series pilot is typically used with one of several different main valves in a pressure relief or backpressure application. This pilot is usually used in gas service. It has an easily-installed valve plug that can be removed without removing the valve plug stem guide.
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