Determining the required valve size
Every system is unique and requires specific engineering
data to correctly size and design. Typically, a valve is
replaced with another valve of the same size.
Important: An undersized valve does not deliver
the required amount of water flow under full load
conditions, and an oversized valve tends to hammer
under low load conditions.
To select the correct valve size, determine the following
variables:
• Maximum water flow required
• Available water pressure drop across the valve, also
known as the differential
Use these variables to locate a point on one of the flow
capacity charts (from Figure 6 to Figure 13) that slightly
exceeds the maximum water flow that you need. The
flow capacity chart that contains this point represents the
correct valve size.
Maximum water flow required
Use the information that the manufacturer of the
condensing unit provides to determine the maximum
water flow that you require. If this information is not
available, calculate the maximum water flow with the
following formula:
Example: If a 100-ton capacity system has an inlet water
temperature of 85°F and an outlet water temperature of
95°F, the maximum water flow that you require is:
Available water pressure drop across the
valve
The available differential, or water pressure drop, across
the valve is the supply pressure to the valve minus all
downstream pressures. This pressure drop is the force
available to push water through the valve.
Water supply pressure is the water supply pressure to the
inlet side of the valve from a cooling tower, a city water
main, or other source.
Figure 2: Pressure drop across the valve
Opening point and refrigerant head
pressure rise
The forces that operate the valve are refrigerant head
pressure, water pressure, and spring pressure. These
forces oppose each other.
When the head pressure rises, and the refrigerant
pressure overcomes the spring force of the pilot valve,
the valve begins to open; the disk lifts off of the seat. This
point is called the opening point.
You can adjust the opening point if you use the
adjustment stem to increase or decrease the spring force.
If the head pressure continues to rise, the refrigerant
pressure further opens the valve until the valve is fully
open. The range from the opening point when the valve
lifts off the seat to the point when the valve is fully open is
called the throttling range.
The throttling range is fixed and you cannot adjust it.
The throttling range is approximately 40 psig for the low-
pressure V43 Series valves, approximately 50 psi for the
medium-pressure V43 Series valves, and approximately 60
psi for the high-pressure V243 Series valves.
Head pressure rise above the opening
point
When the head pressure rises, the force of the refrigerant
head pressure overcomes the spring force and any
hysteresis, and pushes the disc off the seat, facilitating
water to start to flow through the valve.
Anything above that point is head pressure rise above the
opening point. In standard scenarios, the opening point is
approximately 7 psi above the closing point.
V43/V243 Series Pressure-Actuated Water-Regulating Valves Product/Technical Bulletin2
