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Glass &Windows Selection


Two approaches are available for balancing hydronic systems:

(1) a manual valve with integral pressure taps and a calibrated port, which permits field proportional balancing to the design flow conditions;

(2) or an automatic flow-limiting valve selected to limit the circuit’s maximum flow to the design flow.

Manual Balancing Valves

Manual balancing valves can be provided with the following features:

• Manually adjustable stems for valve port opening or a combination of a venturi or orifice and an adjustable valve
• Stem indicator and/or scale to indicate the relative amount of valve opening • Pressure taps to provide a readout of the pressure difference across the valve port or the venturi/orifice
• Capability to be used as a shutoff for future service of the heat transfer terminal

• Locking device for field setting the maximum opening of a valve
• Body tapped for attaching drain hose
Manual balancing valves may have rotary, rising, or nonrising stems for port adjustment

Meters with various scale ranges, a field carrying case, attachment hoses, and fittings for connecting to the manual balancing valve should be used to determine its flow by reading the differential pressure. Some meters employ analog measuring elements with direct-reading mechanical dual-element Bourdon tubes. Other meters are electronic differential pressure transducers with a digital data display.

Manual Balancing Valve

Many manufacturers of balancing valves produce circular slide rules to calculate circuit flow based on pressure difference readout across the balancing valve, its stem position, and/or the valve’s flow coefficient. This calculator can also be used for selecting the size and setting of the valve when the terminal design flow conditions are known.

Automatic Flow-Limiting Valves

A differential pressure-actuated flow control valve, also called an automatic flow-limiting valve, regulates the flow of fluid to a preset value when the differential pressure across it is varied. This regulation (1) helps prevent an overflow condition
in the circuit where it is installed and (2) aids the overall system balance when other components are changing (modulating valves,
pump staging, etc.).

Typically, the valve body contains a moving element containing an orifice, which adjusts itself based on pressure forces so that the flow passage area varies.

The area of an orifice can be changed by either (1) a piston or cup moving across a shear plate or (2) increased pressure drop to squeeze the rubber orifice in rubber grommet valves.

The flow rate for the valve is set. The flow curve is divided into three ranges of differential pressure: the start-up range, the control range, and the above-control range.

Balancing Valve Selection

The balancing valve is a flow control device that is selected for a lower pressure drop than an automatic control valve (5 to 10% of the available system pressure). Selection of any control valve is based on the pressure drop at maximum (design) flow to ensure that
the valve provides control at all flow rates. A properly selected balancing valve can proportionally balance flow to its terminal with
flow to the adjacent terminal in the same distribution zone



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