Powers 597 User Manual

UTILITY IRON BODY SERIES

DESCRIPTION

The rugged Powers Type SI (single seat iron body) balanced valve is primarily
used for steam and water modulating applications with moderate pressure
drops. The equal percent plug provides excellent control characteristics and is
more tolerant of oversizing than linear or quick-opening plugs. The SI’s
control and close off characteristics are particularly well-suited to commercial
water heaters, boilers, and industrial utility applications. The SI balanced valve
is available with the Powers 46 in.

2

and 100 in.2actuators. Actuator selection

depends on valve size and flowing system pressure drop across the valve.

SPECIFICATIONS

VALVE
Body Sizes: 21⁄2" – 6"
Body Material: Cast Iron (per

ASTM A126-93 Class B)

End Connections: 125 # Flanged (per

ANSI B16.1–1993)

Trim: Bronze Composition Disc
Packing: Spring loaded TFE/EPDM packing
Seat Leakage: ANSI Class IV < 0.01% leakage
Close-off Pressure: 125psi
Cv Range: 56-370
Rangeability: 100:1
Characteristics: Equal Percent
Maximum Pressure: 200 psi @ Temp. <150°F
Max. Differential Press.: 50 psi for Bronze
Temperature Range: 40°– 281°F

ACTUATOR
Housing Construction: Die cast aluminum
Diaphragm Construction: Replaceable molded neoprene
Diaphragm Area: 21⁄2" – 5", 46 in.2,

6" – 100 in.

2

Maximum 35 psi and 200°F
Pressure and Temp.:

Ambient Shipping Limits: - 40 to 220

°

F

Ambient Operating Limits: - 20 to 220

°

F

Air Connection:

46 in.2,1⁄4"

NPT

100 in.

2

1

⁄8"NPT

Position Indication:1⁄8"increments
Mounting:

In any upright position with actuator head
above 45° of the center line of the valve
body. Actuator head may be swiveled to any
convenient position.

TABLE OF CONTENTS

Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Application Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Valve Sizing and Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4

Temperature/Pressure Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Dimensional Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Ordering Information

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Sizes Actuators Available

21⁄2" 46 in.

2

Diaphragm

3" 46 in.2Diaphragm
4" 46 in.2Diaphragm
5" 46 in.2Diaphragm
6" 100 in.2Diaphragm

Normally-closed 597 SI with 46 in.2 actuator shown

TI 597SI

TECHNICAL INSTRUCTIONS

Iron Body Series 597 SI

UTILITY IRON BODY CONTROL VALVES

®

Page 2 TI597SI

APPLICATION INFORMATION

Flowrite II Single Seated SI balanced valves are generally recommended for
steam, hot water and chilled water applications. They are particularly
suited for installations requiring tight shutoff and quick response.

THEORY OF OPERATION

On normally closed valve assemblies, the valve stem will start to open
whenever the control air pressure applied against the actuator diaphragm
area and the lower housing exceeds the holding force of the springs. A
further increase in control air pressure will initiate a continued upward
travel of the valve steam until the valve has fully opened.

On normally open valve assemblies, the stem will start to close whenever
the control air pressure applied against the actuator diaphragm area and
upper housing exceeds the holding force of the springs. A further increase
in control air pressure will initiate a continued downward travel of the
valve stem until the valve has fully closed.

The air pressure change to initiate full stem travel is known as the spring
range or span. This spring span is factory set and will vary slightly as the
pressure drop across the valve changes.

When the valve is at its’ “full open” position there is maximum flow
potential through the valve. At this position, valves are compared based
on flow that is directly related to the valve flow coefficient (see Cv
equations in table 1). The 597 SI valves are designed so that equal changes
in valve stem position provide equal percentage changes in existing flow
through the valve. This is otherwise know as an equal percent valve which
has a typical flow curve (figure 2) that can be used to determine flow based
on stem position, pressure drop, and Cv. As you can see from the graph,
these valves are less sensitive at the low end, which gives both high
rangeability and high flows. These types of valves are used extensively to
compensate for fluctuating system requirements (pressure, flow, load, etc.).

Valve actuators equipped with positioners provide feedback for enhanced
control strategies and, as an example, are required for valve staging. Valves
with positioners can utilize full control air pressure at any point in stem
travel to initiate stem movement or to maintain stem position. However,
the actuator springs still provide the necessary force to move the stem in
the opposite direction. Use of a positioner will tend to provide faster
response and ensure repeatability of stem position regardless of the load on
the actuator. However, in a system where available pressure and flow
requirements are relatively consistent, control valves can usually perform
adequately without a positioner.

Figure 1 A- Push to Open

Figure 1 B- Push to Close

Figure 2

TI597SI Page 3

VALVE SIZING AND SELECTION (WATER)

The sizing of a valve is very important if it is to render good service. If it
is "undersized", it will not have sufficient capacity. If it is “oversized”, the
controlled variable may cycle, the trim can be exposed to excessive wear or
wire drawing, and you could expect reduced valve life. To help select the
right valve, it is important to understand your application and its variables
(controlled fluid, temperatures, pressures, min/max load, etc.). When
your system variables are known and you have calculated actual demand, it
is possible to select the right Powers valve for your application. The
following technical data should help you in selecting a valve for your water
control applications. For fluid applications other than water, contact
Powers’ application engineering.

On/Off Control:

These types of applications are normally line sized to reduce pressure drop
and pump size. In these applications it is important to verify valve seat
leakage will not result in system overheat or damage. If this is a concern, it
is necessary to take precautions to alleviate this potential problem.

Proportional Control:

In applications where the close-off pressure at the valve is below 20psig,
use a pressure drop of 5psi.

In applications where the close-off pressure at the valve is above 20psig, it
is generally recommended to take 25-50% of the system pressure drop at
the control valve to maintain good valve/system performance. Certain
applications can successfully utilize lower pressure drops across the valve
(5-25%) if system fluctuations are kept to a minimum. If not, the valve is
considered oversized it will not effectively throttle until it is nearly closed
thereby resulting in poor control.

Refer to the following table for flow….

Table - 1 Water Capacity in Gallons Per Minute

Valve Cv
Size Rating Differential Pressure (ΔP in psi)

5 10 20 30 40 50 60 70 80 90 100 125

2.5 56 125 177 250 307 354 396 434 469 501 531 560 626

385190 269 380 466 538 601 658 711 760 806 850 950

4 145 324 459 648 794 917 1025 1123 1213 1297 1376 1450 1621

5 240 537 759 1073 1315 1518 1697 1859 2008 2147 2277 2400 2683

6 370 827 1170 1655 2027 2340 2616 2866 3096 3309 3510 3700 4137

CAVITATION LIMITATIONS ON VALVE PRESSURE DROP

A concern in high temperature water systems is the potential for cavitation/flashing, which is caused by the downstream pressure being lower than that of the
vapor pressure of the fluid. This basically causes the water to "boil" and can result in reduced flow/capacity, excessive noise, vibration, wear and should be
avoided if possible. Use the following equation to estimate the maximum allowable pressure drop across the valve:

Pmax = 0.5 (P1 – Pv)

Where:

Pmax = Maximum allowable pressure drop
P1 = Absolute inlet pressure (psia)
Pv = Absolute vapor pressure (refer to psia - Table 2)
Absolute pressure = gauge pressure + 14.7

Table-2 Vapor Pressure of Water Table

Water Vapor Water Vapor
Temp. Pressure Temp. Pressure

(°F) (psia) (°F) (psia)

40 0.12 140 2.89

50 0.18 150 3.72

60 0.26 160 4.74

70 0.36 170 5.99

80 0.51 180 7.51

90 0.70 190 9.34

100 0.95 200 11.53

110 1.28 210 14.12

120 1.69 220 17.19

130 2.22 230 20.78