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Type S303

Instruction Manual

Type S303 Relief/Monitor Regulators Form 5036, November 1980

WARNING Fisher regulators must be installed, operated, and maintained in accordance with ferderal, state, and local codes, rules and regulations, and Fisher instructions. If the regulator vents gas or a leak develops in the system, service to the unit may be required. Failure to correct trouble could result in a hazardous condition. Call a gas serviceman to service the unit. Only a qualified person must install or service the regulator. Figure 1. Type S303 relief/monitor regulator



Scope This instruction manual provides instructions and a parts list for Type S303 and S303H gas regulators.

Description Type S303 relief/monitor regulators take the place of two separate service regulators on monitor applications. Intended for intermediate industrial and commercial applicatons, they can be used for pressure reducing service on natural, manufactured, or LP-gas. Two versions are available: S303 with an outlet pressure range of 4 to 28inches w.c. (4 springs) and S303H with an outlet pressure range of 1.0 to 2.25 psig (2 springs).

Specifications Table 1 lists the specifications for Type S303 and S303H constructions. The following information is stamped on the regulator at the factory: type number, date of manufacture, actuator spring range, port size, monitor spring number, and monitor spring range.

Š by Fisher Controls Company 1980

WARNING Personal injury or system damage may result if this regulator is installed, without appropriate overpressure protection, where service conditions could exceed the limits shown in tables 1, 2, and 3 for a given construction. Regulator installations should be adequately protected from physical damage. All vents should be kept open to permit free flow of gas to the atmosphere. Protect openings against entrance of rain, snow, insects, or any foreign material that may plug the vent or vent line. On outdoor installations, point the spring case and monitor casing vent downward to allow condensate to drain (see figure 2). This minimizes the possibility of freezing and of water or other foreign materials entering the vent and interfering with proper operation. Under enclosed conditions of indoors, escaping gas may accumulate and be an explosion hazard. In these cases, the vent should be piped away fom the regulator to the outdoors.

Type S303 Table 1. Specifications


1-1/4, 1-1/2, & 2 inch NPT screwed inlet and outlet


1/4, 3/8, 1/2, 3/4 inches 3/16 inch for S303 only


See table 3


-20째 to +170째 F (-29째 to 77째 C)


4" W.C. to 2.25 psig (10 to 155 millibar)




Approximately 7" W.C. to 1 psig over outlet setting (17 to 69 millibar)


14 pounds (6.4 kg)




Like most regulators, S303 and S303H regulators have an outlet pressure rating lower than their inlet pressure rating. Overpressuring any portion of the regulators beyond the limits in tables 3 and 4 may cause leakage, damage to regulator parts, or personal injury due to bursting of pressure-containing parts.





If the regulator is exposed to an overpressure condition, it should be inspected for any damage that may have occurred. Regulator operation below these limits does not preclude the possibility of damage from external sources or from debris in the pipeline. Before installing the regulator, check for damage which might have occurred in shipment. Also check for dirt or foreign matter which may have accumulated in the regulator body or in the pipeline. Apply pipe compound to the male threads of the pipeline and install the regulator so that flow is in the direction of the arrow cast on the body. The diaphragm casing assembly can be rotated to any position relative to the body. Loosen the two cap screws holding the union ring (key 11, figure 4) in order to rotate the diaphragm casing assembly. Do not install the regulator in a location where there can be excessive water accumulation, such as directly beneath a down spout. The regulator vent is 1 inch FNPT and the monitor vent is 1/ 4 inch FNPT. The vent openings are screened to prevent insects from entering. On outdoor installations, the vent opening must be pointing down, see figure 2, for protection against the elements and to allow condensate to drain. Indoor installations require a separate vent line be run from each vent to a safe outdoor location. The vent lines should be of as large diameter pipe as practical with a minimum number of bends. Remove the vent screen when attaching the piping to the vent. A weather resistant vent assembly, such as Fisher Type Y602, should be installed at the end of each vent piping with the vent assembly opening pointing down. The vent assembly should be in a protected location as explained above for regulators installed outdoors.



Figure 2. Various vent positions A program of regular inspection of the vent opening should be established to see that it has not become plugged by foreign material. On some installations, such as in areas of heavy snow fall, it may be necessary to install the regulator beneath a protective hood. If other protection is provided from the elements, the vent should be pointing or sloping down sufficiently to allow any condensate to drain. It is advisable that the downstream piping be the same size as the regulator outlet for a minimum distance of 18 inches or to the meter inlet. Replace the regulator if water gets into the spring case or the lower casing of the regulator.

STARTUP CAUTION Pressure gauges should always be used to monitor downstream pressure during startup. Procedures used in putting this regulator into operation must be planned accordingly if the downstream system is pressurized by another regulator or by a manual bypass. If the downstream system is not pressurized by another regulator or manual bypass valve, use the following procedure to start-up the regulator. 1. Slowly open the upstream shutoff valve. 2. Slowly open the downstream shutoff valve. 3. Check all connections for leaks.

Type S303 Table 2. Maximum Downstream Pressure and Relief Valve Flow

Type Number



Relief/Monitor Data

Outlet Pressure Range Inches W.C. 4-9.5 8-14 10-20 18-33 .75-1.6 psig 1.25-2.25 psig

Millibar 10-24 20-35 25-50 45-82 52-110 86-155

Maximum Downstream Pressure Psig Millibar 1.0 69 1.25 86 1.8 124 3.0 207 4.0 276 5.0 345

Spring Part Number

Color Code

Number of Spring Seats Required

Maximum Flow Thru Relief Valve, SCFH of 0.6 Sp. Gr. Gas

1L2557 27132 1L2557 27132 1L2558 27132 1L2559 27132 1V2242 27012 1V2242 27012

Green Green Red Blue Cadmium Cadmium

1 2 1 1 1 2

1,000 1,200 1,600 2,000 2,500 3,000

Adjustment To increase the outlet pressure setting of the regulator, the adjusting screw (key 3) must be turned clockwise. This requires removal of the closing cap (key 4). To reduce the outlet pressure setting, turn the adjusting screw counterclockwise. A pressure gauge should always be used to monitor downstream pressure while adjustments are being made. Do not adjust the spring to produce an outlet pressure setting above the limit stamped on the closing cap. If the required pressure is not within the range of the spring being used, substitute with the correct spring as shown in table 5. When changing the spring, also change the closing cap so that the actual pressure range of the spring in use is indicated. After the spring adjustment has been completed, replace the closing cap.

Inches 3/16 1/4 3/8 1/2 3/4

Table 4. Maximum Outlet Pressure Setting Type Maximum Outlet* Number S303 28" W.C. (70 millibar) S303H 2.25 psig (155 millibar) * Maximum emergency outlet (casing) pressure for S303 Series if 15 psig.

SHUTDOWN Installation arrangements may vary, but in any installation it is important that the valves be opened or closed slowly and that the outlet pressure be vented before venting inlet pressure to prevent damage caused by reverse pressurization of the regulator. The steps below apply to the typical installation as indicated.

Table 3. Maximum Inlet Pressure Maximum Inlet Pressure S303 S303H mm Psig Bar Psig Bar 4.8 125 8.6 6.4 125 8.6 125 8.6 9.5 30 2.1 80 5.5 12.7 25 1.7 60 4.1 19.1 15 1.0 40 2.75

Seat Ring Size

Type S303

1. Open valves downstream of the regulator. 2. Slowly close the upstream shutoff valve. 3. Inlet pressure will automatically be released downstream as the regulator opens in response to the lowered pressure on the diaphragm.

PRINCIPLE OF OPERATION As downstream pressure registers under the main diaphragm, it also registers on top of the monitor diaphragm through the pitot tube located near the body outlet, see figure 3. Thus, under normal conditions as downstream pressure fluctuates due to load changes, the main regulator disk and the monitor piston move toward or away from the seat ring. If downstream pressure reaches over-pressure conditions (7 inches w.c. to 1 psig above the outlet pressure settingdepending on the main regulator spring), the internal relief valve opens. At the same time, downstream pressure on the monitor diaphragm moves the monitor piston further into the body, restricting the seat ring. This minimizes further flow


Table 5. Main Spring Pressure Ranges Spring Range Part Number Color Code Inches W.C. Millibar 4.0-6.0 10-15 T11241 27222 Red 5.0-8.5 12.5-21 T11221 27222 Cadmium 8.0-14 20-35 T11236 37022 Blue 12-28 30-70 T11237 27012 Green 1.0-1.6 psig 70-110 T11385 27142 Black 1.5-2.25 psig 103-155 T11384 27142 Olive Drab

through the seat ring and enables the relief valve to relieve the downstream over-pressure conditions. As downstream pressure drops back to normal, the piston moves back away from the seat ring and the relief valve closes, automatically allowing normal operation again. The combination of a restriction in the relief valve and the monitor piston positioned near the inlet side of the seat ring limits the maximum downstream pressure and the related flow through the relief valve to the values shown in table 2.

MAINTENANCE WARNING To avoid personal injury or equipment damage,




adjusting screw slightly. This will align the diaphragm to ensure a smooth seal.

Disassembly to Replace Valve Disk Refer to Figure 4.

1. Remove the two bolts in the union ring (key 11). 2. The spring case and lower casing can be removed from the body. Inspect the body O-ring (key 27) and replace if necessary. INTERNAL RELIEF VALVE ASSEMBLY MAIN REGULATOR DISC


Figure 3. Operational drawing

do not attempt any maintenance or disassembly without first isolating the regulator from system pressure and relieving all internal pressure as described in “Shutdown�. Regulators that have been disassembled for repair must be tested for proper operation before being returned to service. Only parts manufactured by Fisher should be used for repairing Fisher regulators. Relight pilot lights according to normal startup procedures. Due to normal wear or damage that may occur from external sources, this regulator should be inspected and maintained periodically. The frequency of inspection and replacement of parts depends upon the severity of service conditions or the requirements of local, state, and federal rules and regulations.

Disassembly to Replace Main Diaphragm Refer to Figure 4. 1. Remove closing cap (key 4) and turn the adjusting screw out of the spring case. 2. Take the spring (key 2) out of the regulator. 3. Remove the cap screws holding the spring case (key 1) to the lower casing (key 10). Remove the spring case. 4. The diaphragm and diaphragm head assembly (keys 5A & 5C) can be removed by sliding the relief valve seat (key 7) off the lever (key 14). 5. Unscrew the relief valve stem (key 30) from the diaphragm assembly to complete the disassembly. 6. Reassemble in the reverse order of the above procedures. Before tightening stem (key 30) into spring seat (key 6) to secure the new diaphragm, place the loosely assembled diaphragm and head unit into position in the lower casing (key 10), being sure the spring seat is properly hooked on the lever (key 14). Rotate the diaphragm so that the diaphragm and lower casing holes align. Tighten stem (key 30) and proceed with reassembly.

CAUTION Before tightening cap screws on spring case, replace spring and adjusting screw. Tighten 4

3. The valve disk holder (key 19) unscrews from the valve stem (key 17A). Examine the disk for nicks, cuts, and other damage, and replace it if necessary. 4. Reassemble in the reverse order of the above procedure.

Disassembly of Monitor Refer to Figure 4.

1. Remove the four cap screws holding the monitor to the regulator body. 2. Remove the eight screws (key 81) and lift off the monitor spring case (key 76). The diaphragm (key 78) can now be removed. Note When replacing the diaphragm and spring case, carefully align them on the roll pin (key 79). Try to allow as much slack as possible in the diaphragm upon reassembly. 3. Hold the disk holder assembly (key 91B) and turn the diaphragm plate (key 83) off the stem. The spring (key 84) and spring seat (key 85) can now be changed. 4. To inspect piston ring (key 97), push the piston assembly (key 86) out of the guide (key 89) until the ring is exposed slightly.

CAUTION Protect the ring halves because they will eject from the groove if completely exposed due to the ring expander. The piston halves are matched, and caution should be taken when replacing them in the groove. The halves should be placed over the ring expander (key 96) in the piston groove and properly mated. 5. The piston assembly and inside surface of the piston guide (key 89) should be as free of grease and foreign particles as possible to ensure correct operation. 6. The seat disk (key 91A) can be replaced if necessary by removing the disk holder screw (key 92) and the disk retainer (key 98). 7. The stem O-ring (key 88) can be replaced after removal of the retainer (key 87). 8. If the stem O-ring is replaced, make certain the monitor stem threads do not damage the O-ring, resulting in a possible gas leak. 9. On reassembly, check O-ring (key 90) to make certain it is not twisted.

Type S303 10. Tighten cap screws (key 80) evenly as the monitor is replaced on the regulator body.

Treat the male threads of the new seat ring with pipe compound before reassembling.

Disassembly to Replace Seat Ring

6. Reassemble spring case and lower casing and the monitor.

Refer to Figure 4. 1. Remove the two bolts in the union ring (key 11). 2. The spring case and lower casing can be removed from the body.


3. Remove the four cap screws holding the monitor to the regulator body.

The type number, seat ring (por t) size, and date of manufacture are stamped on the closing cap. Always provide this information in any correspondence with your Fisher representative regarding replacement parts or technical assistance. If construction changes are made in the field, be sure that the closing cap is also changed to reflect the most recent construction.

4. Remove seat ring (key 24) by unscrewing the keeper (key 34). 5. If the seating edges of the seat ring are nicked or rough, the seat ring should be replaced to provide proper shutoff.

Figure 4. Type S303


Type S303

Key 1


Part Number

Spring Case Assembly S303 S303H

T11238 000A2 T11389 000A2


Spring, steel, see table 5


Adjusting Screw S303, plastic S303H, aluminum

T11225 06642 T11388 09012

Closing Cap, zinc

T20290 44012


5A* Diaphragm, rubber

T11227 02532

5B* Diaphragm Pad, Rubber

T11210 03162

5C Diaphragm Head, Steel

T20289 25062


Spring Seat, steel

T11793 32982


Relief Valve Seat, Aluminum

T40091 08012



Lower Casing, Aluminum S303 S303H

T80061 08012 T20389 08012

T11216 08012


Split Ring, SST

T11206 37022


Stem Guide, plastic

T20286 06992


Valve Lever, steel S303 S303H

T11205 25062 T11386 25062


Pivot Pin, SST

1E9837 35032


Machine Screw, steel (2 Req’d) S303 S303H

T11214 28982 T11539 28982

Valve Stem Subassembly, Aluminum (Includes 17A & 17B) S303 T11197 00022 S303H T11391 00022

19* Valve Disk & Holder


Part Number


Nut, steel (8 Req’d)

83 23.1 Body Assembly, Cast iron 1-1/4 inch 1-1/2 inch 2 inch

T20434 19012 T20435 19012 T20436 19012

23.2 Pitot Tube, Aluminum

1V2182 09012


Seat Ring, aluminum S303 & S303H: 1/4 inch 3/8 inch 1/2 inch 3/4 inch S303 Only: 3/16 inch


Baffle, aluminum

27* O-Ring, rubber 28



T11796 T11797 T11798 T11800


X0012 X0012 X0012 X0012

T11795 09012

Cap Screw, steel (8 Req’d)

Type S303H Only: For Springs T11385 & T11384 (Cadmium) 85

T11208 28982

Relief Valve Spring, Spring Wire

T11215 27012

Relief Valve Stem, Steel

T11207 24272

1L2557 27132 1L2558 27132 1L2559 27132

1V2242 27012

1U9822 09012

86A Piston, SST

1U9824 35032

86B Monitor Stem, SST

1U9825 35072

86C Drive Pin, SST

1D7991 38992


T11510 11992

O-Ring Retainer, Aluminum

1D1917 06992


T11803 35132

Piston Guide, SST

90* O-Ring, rubber

1V8211 06562

91A* Valve Disk, rubber

1H9738 03022

1H9737 09012

T11801 24102

91B Disk Holder, Aluminum


Pipe Plug, brass

1A6219 14012



Monitor Spring Case, Aluminum

3U9818 08102

Monitor Lower Case, Aluminum

3U9819 08012

78* Diaphragm, Rubber

1U9820 02052


Roll Pin, steel

1R1396 28992


Cap Screw, steel, (4 Req’d)

1U9836 09012

88* O-Ring, rubber

Keeper, steel

Disk Holder Screw, Aluminum

T11802 X0012


Vent Assembly


Pipe Plug, steel

1A6219 14012


Piston Ring Expander, SST

1V3434 38992

97* Ring, rubber 98

Cap Screw, steel, (8 Req’d)

2U9821 08012

T11211 06992

Type Y602-12

1V3433 05102

Disk Retainer, Aluminum

1V6099 09012

Vent Screen, SST

T11213 38982

Retaining Ring, steel

T11209 25072

1A3418 24052

1A3917 24052

*Recommended Spare Parts

Fisher Controls Company, Marshalltown, Iowa,.

Lower Spring Seat, Aluminum



Fisher Controls

Monitor Spring, steel Type S303 Only: For Springs T11241, T11221 & T11236 (Green) For Spring T11237 (Red) For Spring T11237 (Blue)

1E1056 06992

T12523 T0012

T10708 48322

Diaphragm Plate, Aluminum

33* Closing Cap Gasket, Rubber


1H2924 06992

T11229 11992

Cap Screw, steel (2 Req’d)

Slip Disk, aluminum S303H Only

Part Number

1E9853 24142

99 21


82* O-Ring, rubber 22


Union Ring, Aluminum




Specifications are subject to change. Metric equivalents of English units are shown in parentheses and are in millimeters unless otherwise noted.

Printed in U.S.A.


S303 Instruction Manual