ASHRAE Journal - April 2013 - 49

Cv is numerically equal to the number
of U.S. gallons (liters) of water at 60°F
(20°C) that will flow through the valve in
one minute when the pressure differential
across the valve is 1 lb/in.2 (1 kPa).
Cv varies with size and style of valve,
which provides an index for comparing
liquid capacities of different valves under
a standard set of conditions.
Knowing the control valve Cv (from
valve submittals) and the design flow, it
is easy to calculate the required pressure
drop across the control valve and verify
it with a water meter. Therefore, it is
possible to set design flow using control
valve Cv.
Automatic Flow-Control Valve. Automatic flow-control valves regulate the
flow of fluid, such as water, to a design
value. When the differential pressure
across it is varied, the automatic flow
control usually has a spring-loaded cartridge that dynamically absorbs pressure
fluctuations, resulting from changing
flow conditions, valve modulation, etc.
These fluctuations in pressure, within a
given pressure differential control range,
do not change the flow through the valve.
A typical performance curve for the valve
is shown in ASHRAE Handbook–HVAC
Systems and Equipment, Chapter 47,
Figure 22 (shown here as Figure 3).
The flow curve is divided into three
ranges of differential pressure: the

Conclusions and recommendations
Consider the joint operation of the
control valve, which keeps regulated
process variable, as shown in Figure 2,
and the automatic flow-control valve is
controlling constant flow, as shown in
Figure 3.
When the control valve is fully open,
the automatic flow-control (limiting)

Start-Up Range

160
140

Control
Range

120
rated Flow (%)

start-up range, the control range, and
the above-control range. At the startup range of differential pressure, the
spring-loaded cartridge is fully open
and cannot control the flow. At the
above-control range of differential
pressure, the spring-loaded cartridge
is at maximum closed position and
cannot control the flow. Only in the
control range of differential pressure is
the spring-loaded cartridge controlling
constant flow to within ±5%.
Manual-Balancing Valve. Manual
balancing valves allow the measurement
of differential pressures that can be
used to calculate and set a determined
flow. By measuring the pressure drop
across measuring ports at a particular
hand-wheel setting, the water flow for
the valve size can be easily read from
the appropriate pressure drop graph or
flow-balancing wheel. All balancing
valves include a memory feature with a
locking setting.

Above-Control
Range
± Accuracy Band

100
80
ed
Fix

60

t
Por

40
20
0

Variab
le

Port
rv

rs
Differential Pressure

Figure 3: Automatic flow-limiting valve curve.
April 2013

www.info.hotims.com/44631-14

ASHRAE Journal

49



ASHRAE Journal - April 2013

Table of Contents for the Digital Edition of ASHRAE Journal - April 2013

ASHRAE Journal - April 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Ground-Coupled Heat Pump and Energy Storage
Fan Efficiency Requirements for Standard 90.1-2013
Technology Award Case Studies:
Geothermal for 5 Ecosystems
Holistic HVAC Design
Standing Columns
Engineer’s Notebook
Data Centers
Emerging Technologies
IAQ Applications
Refrigeration Applications
Special Products
People
International Column
Energy Modeling
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2013 - ASHRAE Journal - April 2013
ASHRAE Journal - April 2013 - Cover2
ASHRAE Journal - April 2013 - 1
ASHRAE Journal - April 2013 - 2
ASHRAE Journal - April 2013 - Contents
ASHRAE Journal - April 2013 - Commentary
ASHRAE Journal - April 2013 - 5
ASHRAE Journal - April 2013 - Industry News
ASHRAE Journal - April 2013 - 7
ASHRAE Journal - April 2013 - 8
ASHRAE Journal - April 2013 - Letters
ASHRAE Journal - April 2013 - Meetings and Shows
ASHRAE Journal - April 2013 - 11
ASHRAE Journal - April 2013 - 12
ASHRAE Journal - April 2013 - 13
ASHRAE Journal - April 2013 - Ground-Coupled Heat Pump and Energy Storage
ASHRAE Journal - April 2013 - 15
ASHRAE Journal - April 2013 - 16
ASHRAE Journal - April 2013 - I1
ASHRAE Journal - April 2013 - I2
ASHRAE Journal - April 2013 - I3
ASHRAE Journal - April 2013 - I4
ASHRAE Journal - April 2013 - 17
ASHRAE Journal - April 2013 - 18
ASHRAE Journal - April 2013 - 19
ASHRAE Journal - April 2013 - 20
ASHRAE Journal - April 2013 - 21
ASHRAE Journal - April 2013 - 22
ASHRAE Journal - April 2013 - 23
ASHRAE Journal - April 2013 - Fan Efficiency Requirements for Standard 90.1-2013
ASHRAE Journal - April 2013 - 25
ASHRAE Journal - April 2013 - 26
ASHRAE Journal - April 2013 - 27
ASHRAE Journal - April 2013 - 28
ASHRAE Journal - April 2013 - 29
ASHRAE Journal - April 2013 - 30
ASHRAE Journal - April 2013 - 31
ASHRAE Journal - April 2013 - Geothermal for 5 Ecosystems
ASHRAE Journal - April 2013 - 33
ASHRAE Journal - April 2013 - 34
ASHRAE Journal - April 2013 - 35
ASHRAE Journal - April 2013 - 36
ASHRAE Journal - April 2013 - 37
ASHRAE Journal - April 2013 - 38
ASHRAE Journal - April 2013 - 39
ASHRAE Journal - April 2013 - Holistic HVAC Design
ASHRAE Journal - April 2013 - 41
ASHRAE Journal - April 2013 - 42
ASHRAE Journal - April 2013 - 43
ASHRAE Journal - April 2013 - 44
ASHRAE Journal - April 2013 - 45
ASHRAE Journal - April 2013 - 46
ASHRAE Journal - April 2013 - 47
ASHRAE Journal - April 2013 - Engineer’s Notebook
ASHRAE Journal - April 2013 - 49
ASHRAE Journal - April 2013 - 50
ASHRAE Journal - April 2013 - 51
ASHRAE Journal - April 2013 - 52
ASHRAE Journal - April 2013 - 53
ASHRAE Journal - April 2013 - Data Centers
ASHRAE Journal - April 2013 - 55
ASHRAE Journal - April 2013 - 56
ASHRAE Journal - April 2013 - 57
ASHRAE Journal - April 2013 - 58
ASHRAE Journal - April 2013 - 59
ASHRAE Journal - April 2013 - Emerging Technologies
ASHRAE Journal - April 2013 - 61
ASHRAE Journal - April 2013 - 62
ASHRAE Journal - April 2013 - 63
ASHRAE Journal - April 2013 - IAQ Applications
ASHRAE Journal - April 2013 - 65
ASHRAE Journal - April 2013 - 66
ASHRAE Journal - April 2013 - Refrigeration Applications
ASHRAE Journal - April 2013 - Special Products
ASHRAE Journal - April 2013 - People
ASHRAE Journal - April 2013 - International Column
ASHRAE Journal - April 2013 - 71
ASHRAE Journal - April 2013 - Energy Modeling
ASHRAE Journal - April 2013 - 73
ASHRAE Journal - April 2013 - Products
ASHRAE Journal - April 2013 - 75
ASHRAE Journal - April 2013 - 76
ASHRAE Journal - April 2013 - 77
ASHRAE Journal - April 2013 - 78
ASHRAE Journal - April 2013 - Classified Advertising
ASHRAE Journal - April 2013 - Advertisers Index
ASHRAE Journal - April 2013 - Cover3
ASHRAE Journal - April 2013 - Cover4
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