98 Series Backpressure Regulators
and Relief Valves
W6155
TYPE 98H
W6157
TYPE 98LD
November 2009
W6158
TYPE 98HD
Figure 1. Typical 98 Relief Valves
Introduction
The 98 Series (Figure 1) is used for backpressure
or relief applications in liquid, gas, air, and steam
service. The Types 98L, 98H, and 98HH are directoperated and spring-loaded. The Types 98LD and
98HD use additional pressure loading to maintain relief
differential pressures, backpressures or for remote
setpoint adjustment.
The Type 98HM is a direct-operated, spring to close
regulator for backpressure or relief applications in
liquid, gas, or steam service. The regulator requires
no external power to operate and features a sensing
line connection for sensing pressure externally from
the regulator. A seal washer for the set screw can be
included when applications require pressure loading
of the spring case (not available on NPS 1-1/2 and 2
bodies (DN 40 and 50)).
Using a Type 98HM as a relief valve does not
exclude the installation of an ASME certied
full ow valve as specied by local codes and
regulations or system design.
W6156
TYPE 98L
Features
• Versatility—Typical applications include
backpressure on pumps, maintaining differential
pressure across lubricated seals, steam header
pressure, fuel and oil lines, air supply systems,
pump bypass applications for API general and
special purpose lube and seal oil systems, relief
applications for ash tanks and accumulators, and
other process and industrial uses.
• Excellent Fluid Compatibility—Diaphragms come
in stainless steel, Monel®, Hastelloy® C, or elastomers,
and body is available in cast iron and steel as well as
stainless steel, Hastelloy® C, and Monel®. Corrosion resistant trims are available.
• Close, Stable Regulation—Diaphragm is isolated
from the main ow stream. Slotted valve plug and
pusher post assembly provides positive guiding for
improved shutoff.
• Compact Design—Small size allows easy
installation in limited spaces.
Hastelloy® C is a mark owned by Haynes International, Inc.
Monel® is a mark owned by Special Metals Corporation.
D100153X012
www.sherregulators.com
Bulletin 71.4:98
Specications
Available Constructions
Type 98L: Direct-operated low-pressure
backpressure/relief valve with internal pressure
registration and standard adjusting screw for
2 to 38 psig (0,14 to 2,6 bar) set pressure range
Type 98LD: Pressure-loaded low-pressure
backpressure/relief valve with internal pressure
registration and handwheel adjustment for 2 to 38 psi
(0,14 to 2,6 bar) differential set pressure range
Type 98H: Direct-operated high-pressure
backpressure/relief valve with internal pressure
registration and standard adjusting screw for
5 to 200 psig (0,35 to 13,8 bar) set pressure range
Type 98HD: Pressure-loaded low-pressure
backpressure/relief valve with internal pressure
registration and handwheel adjustment for
5 to 200 psi (0,35 to 13,8 bar) differential set
pressure range
Type 98HH: Direct-operated high-pressure
backpressure/relief valve with internal pressure
registration and standard adjusting screw for 150 to
375 psig (10,3 to 25,9 bar) set pressure range
Type 98HHD: Pressure-loaded high-pressure
backpressure/relief valve with internal pressure
registration and handwheel adjustment for
150 to 375 psi (10,3 to 25,9 bar) differential set
pressure range
Type 98HM: Direct-operated high-pressure
backpressure/relief valve with external pressure
registration and standard adjusting screw for 5 to
275 psig (0,35 to 19,0 bar) set pressure range
Shutoff Classication Per ANSI/FCI 70-3-2004
Metal Seats: Class IV
PTFE: Class IVElastomer Seats: Class VI
Flow Coefcient
C1: 35
Type 98HM Sensing Line Connection
1/2, 1-1/2, or 2 NPT body: 1/8 NPT
3/4 or 1 NPT body: 1/4 NPT
IEC Sizing Coefcients
BODY SIZES,
NPS (DN)
1/4
1/2 (15)0.830.69
3/4 and 1
(20 and 25)
1-1/2 and 2
(40 and 50)
Capacities
Types 98L and 98LD: See Tables 3 through 7
Types 98H and 98HD: See Tables 8 through 12Type 98HH and 98HHD: See Tables 13 through 17Type 98HM: See Tables 18 through 21
Options
• Handwheel or tee handle for Types 98L, 98H,
and 98HH
• Tapped spring case vent for Types 98L, 98H,
98HH, and 98HM
• Seal washer to permit spring case pressure
loading for Types 98L, 98H, 95HH, and 98HM
1. The pressure/temperature limits in this Bulletin and any applicable standard limitation should not be exceeded.
2. Loading pressure plus spring setting should not exceed maximum inlet pressure.
5. Pressure and/or the body end connection may decrease these maximum temperatures.
7. Not available for Type 98HM.
X
T
0.780.50
F
D
F
L
0.910.83
0.880.77
0.920.85
K
m
• Differential Pressure Capability—Spring-loaded
PTFE packing and tapped connections permit
pressure loading of Types 98LD and 98HD
spring cases.
• Handwheels—Handwheels (standard on the
Types 98LD and 98HD and optional on some
sizes of the Types 98L and 98H) allow easy
pressure setting changes.
• Sour Gas Service Capability—Optional
materials are available for applications handling
sour gases. These constructions comply with
the recommendations of NACE International
Standards MR0175 and MR0103.
Principle of Operation
Relief or backpressure valves respond to changes in
upstream pressure. Pressure changes register under
the diaphragm (see Figure 2) through a registration
hole in the valve body (through upstream sensing
line connection for Type 98HM). When the pressure
increases beyond the spring setting, the diaphragm
pressure overcomes the spring compression. This
causes the valve plug to move away from the orice.
The ow line through the valve is open and excess
pressure is vented. When upstream pressure drops
back to normal, the valve resumes its closed position.
The chart in Figure 3 illustrates the operation of an
NPS 1/2 (DN 15) body used in air service. As the
inlet pressure increases, initial ow occurs at the
bubble point of 10.5 psig (0,72 bar). Flow increases
with further rises in the inlet pressure, reaching
500 SCFH (13,4 Nm3/h) at the relief pressure setting
of 12 psig (0,83 bar). Greater capacities are obtained
with higher build-ups over the relief pressure setting,
as shown in the capacity tables.
When the inlet pressure decreases, ow decreases until
the valve reseals to reseat point of 9 psig (0,62 bar).
3
Bulletin 71.4:98
METAL DIAPHRAGMS
SPRING
REGISTRATION
HOLE
ORIFICE
INLET PRESSURE
OUTLET PRESSURE
ATMOSPHERIC PRESSURE
A6925
GASKET
DIAPHRAGM
FOR TYPE 98H WITH TWO METAL DIAPHRAGMS
VALVE PLUG
COMP
O-RING SEAT
(ALSO TYPICAL OF 98HH AND 98L EXCEPT FOR
TYPE 98L, 1/4 NPT, 2 TO 7 PSI (0,14 TO 0,48 bar) RANGE)
SPRING
GASKET
TYPE 98L (1/4 NPT, 2 TO 7 PSI (0,14 TO 0,48 bar) RANGE)
WITH ONE METAL DIAPHRAGM
METAL DIAPHRAGMS
TYPE 98H (ALSO TYPICAL OF 98L AND 98HH)
HANDWHEEL
CONTROL SPRING
VALVE PLUG GUIDE
INLET PRESSURE
OUTLET PRESSURE
LOADING PRESSURE
M1005
Figure 2. 98 Series Operational Schematic
4
SPRING
FOR TYPE 98HD/LD/HHD WITH TWO METAL DIAPHRAGMS,
ASSEMBLE DIAPHRAGM GASKETS UNDER AND ABOVE
THE METAL DIAPHRAGMS AS SHOWN ABOVE
TYPE 98HD (ALSO TYPICAL OF 98LD AND 98HHD)
METAL DIAPHRAGMS
GASKET
M1155
TO UPSTREAMSENSING LINE
Type 98HM
SPRING
Bulletin 71.4:98
METAL DIAPHRAGMS
TO UPSTREAM
SENSING LINE
INLET PRESSURE
OUTLET PRESSURE
ATMOSPHERIC PRESSURE
M1155
TYPE 98HM
Figure 2. 98 Series Operational Schematic (continued)
Once the valve has resealed, leakage will not occur
again until the bubble point pressure of 10.5 psig
(0,72 bar) is reached.
Table 22 shows typical pressure differences between
the relief pressure setting and the bubble point, and
between the relief pressure setting and the reseat
point. These differences are to be used in conjunction
with the capacity tables to determine the total inlet
pressure increase required to develop the tabulated
ows and to determine the actual inlet pressure
reductions required for reseat point.
Capacity Information
GASKET
FOR TYPE 98HM WITH TWO METAL DIAPHRAGMS,
ASSEMBLE DIAPHRAGM GASKETS UNDER AND ABOVE
THE METAL DIAPHRAGMS AS SHOWN ABOVE
Then, if capacity is desired in normal cubic meters per
hour at 0°C and 1,01325 bar, multiply SFCH by 0.0168.
Typical relieving capacities in pounds per hour and
kilogram per hour of saturated steam are shown in
Tables 5, 10, and 15.
Tables 3, 4, 8, 9, 13, 14, 20, and 21 gives relieving
capacities in U.S. gallons per minute and in liters per
minute of water.
Sizing
Determine Flow Rates for units used as differential relief
valves as follows:
Relieving capacities at selected pressures and outlet
pressure ows are given in SCFH (60°F and 14.7 psia)
of air in Tables 6, 7, 11, 12, 16, 17, 18, and 19. To
determine the equivalent capacities for other gases,
multiply the table capacities by the following appropriate
conversion factors: 1.29 for 0.6 specic gravity natural
gas, 0.808 for propane, 0.707 for butane, or 1.018 for
nitrogen. For gases of other specic gravities, divide by
the square root of the appropriate specic gravity.
Air and Steam Service
When the Capacity Information section do not cover
the actual service conditions, it will be necessary to
calculate the ow rate available from the relief valve.
Step 1.
From the Capacity Information section determine a
ow rate using the closest available data for setpoint
5
Bulletin 71.4:98
and build-up. With this information, calculate a ow
coefcient using the following:
Equation 1:
Q
=
C
g
520
GT
P1aSIN
3417
)
C
∆P
DEG
P
)
1a
1
Cg = Calculated Flow coefcient
Q = Flow rate from tables (SCFH)
P
= Inlet pressure from table (set pressure and
1a
build-up) converted to absolute pressure
G = Specic gravity
T = Absolute temperature of gas at inlet
degrees Rankine = °F + 460
P1 = Absolute inlet pressure, psia = psig + 14.7
C1 = 35
∆P = P1 - P2, psid
Calculate the Cg coefcient for the setting and build-up
nearest to the desired service conditions within the
selected spring range. Then use this Cg to calculate
the approximate ow available for the actual setpoint
and build-up desired. Available Cg will vary based
upon setpoint, differential pressure, build-up, and
spring range.
Step 2.
Calculate the actual ow rate available using the
coefcient from Step 1 and the actual inlet pressure
(setpoint plus build-up) and actual outlet pressure
(if not atmospheric).
16 (1,1)
14 (0,97)
12 (0,83)
10.5 (0,72)
10 (0,69)
9 (0,62)
8 (0,55)
INLET PRESSURE, PSIG (bar)
6 (0,41)
A1309-1
Figure 3. Typical Bubble Point and Reseat Point Performance
BUBBLE
POINT
TIGHT
SHUTOFF
POINT
0
AIR FLOW, STANDARD CUBIC FEET PER HOUR (Nm3/h)
500 (13,4)1000 (26,8)1500 (40,2)
and
12 PSIG (0,83 bar) RELIEF
SETTING 500 SCFH (13,4 Nm3/h)
FLOW AT RELIEF SETTING
NPS 1/2 (DN 15) TYPE 98L
INCREASING INLET PRESSUREand
DECREASING INLET PRESSURE
From Table 11, select NPS 3/4 or 1 (DN 20 or 25)
body, red spring for 100 psi (6,9 bar) setpoint, and
10 psi (0,69 bar) build-up. The Type 98H will ow
13 000 SCFH (348 Nm3/h) air.
Calculate Cg for these table conditions using Equation 1:
P1 = 100 psig (6,9 bar) + 10 psig (0,69 bar)
build-up = 110 psig or 124.7 psia (7,6 bar g or 8,6 bar a)
Answer from Equation 2, Q = 14 500 SCFH
(389 Nm3/h) rated capacity. Since this capacity is
greater than the 13 200 SCFH (354 Nm3/h) required,
the relief valve may be used or the calculation could be
repeated to try for a smaller body size.
Example 2.
Service Conditions:
Setpoint, 165 psi (11,4 bar)
Build-up allowed, 10 psi (0,69 bar)
Outlet discharges into pressured system of
50 psi (3,4 bar)
Require 3000 SCFH (80,4 Nm3/h) air ow rate
From Table 11, select NPS 3/4 or 1 (DN 20 or 25)
body, blue spring. For 150 psi (10,3 bar) setpoint and
10 psi (0,69 bar) build-up, the Type 98H will ow
9000 SCFH (241 Nm3/h) air.
Calculate Cg for these table conditions using Equation 1:
Answer from Equation 2, Q = 9500 SCFH (255 Nm3/h)
rated capacity. Since this capacity is greater than the
3000 SCFH (80,4 Nm3/h) required, the relief valve may
be used or the calculation could be repeated to try for a
smaller body size.
Liquid Sizing for Liquids Other than Water
Step 1.
Determine Cv at build-up conditions of application.
Cv =
Q = Flow in GPM from capacity tables
∆P = Pressure drop in psi (setpoint and build-up)
Cv = Valve sizing coefcient
Q
∆P
Step 2.
To determine ow rate for liquids other than
water or ow rate for differential relief service:
Q = Cv ∆P/G
G = Specic gravity of uid
Answer from Equation 1, Cg = 51.5*
*Since build-up relates to travel, this coefcient is
valid for all pressure settings on the spring used in the
calculation whenever the build-up is 10 psi (0,69 bar).
Now, solve for actual ow, Q, from the original service
conditions using Equation 2:
P1 = 165 psig (11,4 bar) + 10 psig (0,69 bar)
build-up = 175 psig or 189.7 psia
(12,1 bar g or 13,1 bar a)
∆P = P1 - P2 = 170 psig (11,7 bar) - 50 psig
(3,4 bar) = 120 psid (8,3 bar d)
Cg = 51.5 (from above)
C1 = 35
Maximum Allowable Pressure Drop for
Liquid Service
Pressure drops in excess of allowable will result in
choked ow and possible cavitation damage.
To determine maximum allowable pressure drop
for water:
∆P(allow) = Km (P1)
∆P = Valve differential - PSI
K
m
P1 = Valve inlet pressure psig
To determine maximum allowable pressure drop for
uids other than water, see Fisher® Catalog 10.
= Valve recovery coefcient from table
7
Bulletin 71.4:98
Table 1. Trim Materials
ELASTOMER SEATSTANDARDOPTIONAL
Orice
O-ring retainer
Valve plug
Valve plug guide
Pusher post
Diaphragm retaining washer
Diaphragm
O-ring seat
METAL SEATSTANDARDOPTIONAL
Orice
Valve plug
Valve plug guide
Pusher post
Diaphragm
Diaphragm retaining washer
1. Available for Type 98HM only.
2. Two metal diaphragms will be used except only for Type 98L, 1/4 NPT, 2 to 7 psi (0,14 to 0,48 bar) range which uses only one metal diaphragm (see Figure 2 for assembly reference).
3. Two diaphragms will be used if elastomer diaphragm is Fluorocarbon (FKM)
Table 2. Spring Ranges for Relief or Differential Relief Pressures
Type 98L or 98LDType 98H, 98HD, or 98HMType 98HH or 98HHD
(1)
, PSIG OR PSI (bar)
SPRING PART NUMBERSPRING COLOR
2 to 7 (0,14 to 0,48 bar)15 to 35 (1,0 to 2,4 bar)- - - -1E392527022Yellow
6 to 14 (0,41 to 0,97 bar)25 to 75 (1,7 to 5,2 bar)- - - -1E392627012Green
(2)
1/4
12 to 25 (0,83 to 1,7 bar)70 to 140 (4,8 to 9,7 bar)- - - -1E392727142Red
20 to 38 (1,4 to 2,6 bar)130 to 200 (9,0 to 13,8 bar)- - - -1L346127142Blue
- - - -- - - -150 to 375 (10,3 to 25,9)1N942227142Light Gray
2 to 7 (0,14 to 0,48 bar)15 to 35 (1,0 to 2,4 bar)- - - -1E395627022Yellow
6 to 14 (0,41 to 0,97 bar)25 to 75 (1,7 to 5,2 bar)- - - -1D7455T0012Green
12 to 25 (0,83 to 1,7 bar)70 to 140 (4,8 to 9,7 bar)- - - -1E395727192Red
1/2 (15)
20 to 38 (1,4 to 2,6 bar)130 to 200 (9,0 to 13,8 bar)- - - -1L380027142Blue
- - - -15 to 100
- - - -100 to 275
(3)
(1,0 to 6,9 bar)- - - -14B9943X012Unpainted
(3)
(6,9 to 19,0 bar)- - - -14B9942X022Unpainted
- - - -- - - -150 to 375 (10,3 to 25,9)1N943427142Light Gray
2 to 7 (0,14 to 0,48 bar)15 to 35 (1,0 to 2,4 bar)- - - -1E398927022Yellow
6 to 14 (0,41 to 0,97 bar)25 to 75 (1,7 to 5,2 bar)- - - -1E399027142Green
12 to 25 (0,83 to 1,7 bar)70 to 140 (4,8 to 9,7 bar)- - - -1E399127162Red
3/4, 1
(20, 25)
20 to 38 (1,4 to 2,6 bar)130 to 200 (9,0 to 13,8 bar)- - - -1L380127082Blue
- - - -15 to 100
- - - -100 to 275
(3)
(1,0 to 6,9 bar)- - - -14B9944X022Unpainted
(3)
(6,9 to 19,0 bar)- - - -14B9945X022Unpainted
- - - -- - - -150 to 375 (10,3 to 25,9)1N944127182Black Stripe
- - - -5 to 35 (0,34 to 2,4 bar)- - - -1E792327092Dark Gray
1-1/2, 2
(40, 50)
- - - -20 to 65 (1,4 to 4,5 bar)- - - -1E795327082Light Blue
- - - -50 to 100 (3,4 to 6,9 bar)- - - -1E795427082Light Gray
- - - -80 to 170 (5,5 to 11,7 bar)- - - -1P788827082Black
1. All springs may be backed off to 0 psig (0 bar). However, highest capacities and best performances are obtained by using these springs in their recommended ranges. Psi rather
than psig are used for differential relief constructions.
2. Not available for Type 98HM.
3. Only available for Type 98HM. Stainless steel construction.
8
Bulletin 71.4:98
Table 3. Water Relief Capacities in Gallons per Minute (l/min), Types 98L and 98LD with Elastomer Diaphragm