Steam Pressure
Reduction Stations
Best practices lead to less maintenance,
downtime and energy loss.
Kevin Arcuri – The John N. Fehlinger Co.
in conjunction with – Warren Controls, Inc.
Function:
Maintain a reduced
pressure under a range
of flow conditions.
100
10
10,000 # / Hr.
Why are Steam Reducing
Valves Required?
• Satisfy load requirements of steam
consuming equipment
• A variety of pressures may be required
Properties of Steam
• Compressibility
Volume Occupied by a
Pound of Steam
Specific
Volume
27.0
Ft3 / lb
3.9
100
psig
17.8
6.8
50
psig
10
psig
Atmosphere
Properties of Steam
• Large Quantities of Heat Available
970 BTU / Lb.
Latent Heat at Atmosphere
Properties of Steam
• Enthalpy remains close to constant during
reasonable pressure reductions
100 PSIG
10 PSIG
Total Heat = 1189 BTU / Lb.
Total Heat = 1160 BTU / Lb.
Latent Heat = 880 BTU / Lb.
Latent Heat = 952 BTU / Lb.
Sensible Heat = 309 BTU / Lb.
Sensible Heat = 208 BTU / Lb.
3.9 Ft3 / Lb.
16.2 Ft3 / Lb.
338˚F
239˚F
Saturation Temp 10 PSIG, approx 239˚F
Terminology
1. Accuracy of Regulation – expressed
as a percent of controlled pressure.
i.e. 90% accuracy means 10% error
from set point to achieve rated valve
capacity
Terminology
2. a) Reverse Acting – an increase in
measured variable produces a
decrease in signal output.
b) Direct Acting – an increase in
measured variable produces an
increase in signal output.
Terminology
3. Normally Closed or Open – Position of
valve on loss of operating medium.
Terminology
4. Flow Coefficient Cv – A dimensionless
number defined as 60˚F water flowing at
1 gallon / minute with a 1 PSI pressure drop
across the controlled element (valve).
Valves are rated for capacity by a Cv number
in a prescribed ISA test procedure.
Terminology
5. Supply Pressure Effect – The change in
controlled set point caused by change in
supply pressure, usually expressed as a ratio
of the two pressures.
Example:
10 to 1 ratio can mean for
every 10 PSI change in supply
pressure the set point changes
by 1 PSI.
Terminology
6. a) Turndown – The range of flow over
which a valve must operate.
b) Rangeability – The ratio of
maximum rated flow of a valve
divided by its minimum controllable
flow as stated by the manufacturer.
Terminology
7. a) Dead End Service – A process which at
times will require zero flow and complete
closure of the valve.
b) Seat tightness – The degree of leakage
permissible across a closed valve as
defined by ANSI. Five classes range
from 0.5% to zero leakage.
c) Steam Tight – Generally accepted as
ANSI Class IV shut off with 0.01%
permissible leakage.
Terminology
8. a) Pressure Boundary – Those valve parts
which contain the line pressure and prevent
it from reaching atmosphere.
b) Trim – The internal valve parts that
throttle the flow. Usually the valve plug,
stem, seat and cage.
c) Actuator – The assembly which provides
the force to operate the valve.
Design Features
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•
•
•
•
•
ANSI Face to Face
ANSI Leakage Class
Serviceability (Cage Trim)
Actuator Maintenance
Flow Capacity
Pressure Drop Capability
PRV Station Design
Considerations
•
•
•
•
•
•
Function
Sizing (By Mfg’s Programs)
Piping
Turndown Requirements
Safety
Noise
Typical: Major PRV Station
1. Continuous Service (Heating, A/C & DHW
a)
b)
c)
d)
Design Load 15,000 Lbs./Hr.
Minimum Load – Dead End
Supply Pressure 150 PSIG Nominal
Outlet Pressure 12 – 15 PSIG
2. Location of PRV Station
a) Basement Mechanical Space
b) Community Center above ( 80 dBA Limit )
3. Safety Issues
a) Relief Valve Venting Difficulty
Type of System
1. Turndown approaching 100 : 1
a) 1/3 – 2/3 ( Lead / Lag )
b) Split Range Systems
c) Transfer ( Switching Systems )
Safety - Relief valve sizing
N
( 4” x 6” )
P
( 4” x 6” )
Q
( 6” x 8” )
Set Pr
3%
10%
3%
10%
10
4899
5032
7202
7398
12470 12808 17950 18442
15
5808
6109
8685
8991
15040 15549 21650 22389
20
6917
7186
10170 10565 17600 18290 25350 26336
Vent Line 10”
Drip Pan Elbow 8”
Exhaust Header 16,000 # / Hr. (10”)
3%
10%
R
( 6” x 8” )
3%
Set Pressure
15 psig
Q orifice
6x8 R.V.
Cap 15,549
10%
System Protection
1. Relief Valve
( Difficult to vent out of the Building )
2. ASME Code B31.1 permits elimination of
a relief valve if two stage reduction is
used, if both stages can be set at the safe
working pressure of the equipment being
served or if single stage reduction is used
with a trip stop shut off valve.
a) Single Stage (No Redundancy)
b) Two Stage – with Safety Shut Off
Pipe Sizing ≈
6,000 to 8,000 ft / min
Max Steam
Flow # / Hr.
Steam Pressure (PSIG)
5
10
20
40
60
80
100
150
10,000
10
8
8
6
5
5
4
4
12,000
10
10
8
6
6
5
5
4
14,000
12
10
8
8
6
5
5
4
16,000
12
10
10
8
6
6
5
5
Inlet Pipe 4”
Outlet Pipe 8”
Prediction Method
Flow Factor
Decibels
∆P / P1 Factor
83
+10
73
Low
High
Flow
Flow
Flow Rate Lbs. / Hr.
SPL = 83 dBA
Resultant Noise = 93 dBA
= 83 dBA
Pressure Drop Ratio
SPL = 10 dBA
(High Flow)
(Low Flow)
Noise Attenuation Options
•
•
•
•
Silencer – 20 dBA
Diffuser – 5 to 7 dBA
Acoustic Insulation – 5 to 10 dBA / Inch
Schedule 80 Pipe – 3 to 5 dBA
Additional Safety
Automatic Shut Down Valve
Manual
Reset SW
HP
Steam
PRV Station
LP
Steam
SSO
T
120
VAC
Vent
To SSO
Review of Advantages to
2-Stage Parallel Reducing Stations
1. If one stage fails the other stage
automatically takes full pressure drop
2. The rangeability of the valve system is
increased to 130 : 1
3. Pneumatically operated controls require
less maintenance than steam pilots
4. Valves fail closed on loss of signal
Review of Advantages to
2-Stage Parallel Reducing Stations
5. Relief Valve, outside vent pipe and exhaust
head can be eliminated.
6. Overall Installed cost can be less.
7. Best overall design for safety, recovery
from event, longevity of components,
installed system noise and controlled set
point over a broad range of loads.
In Closing…
• Please stop by the Warren Controls
booth during your next break for further
questions and a copy of ValveWorks®
control valve sizing & selection software.
• Thank you for your attention.