Pressure-reducing valves for heating equipment and accessories

1. Commonly used pressure-reducing valves include piston-type, diaphragm-type, bellows-type, and water supply pressure-reducing valves.

2. Flow calculation for pressure-reducing valves: The critical pressure ratio is the key factor in determining the flow rate of a steam pressure-reducing valve. Different calculation methods are used to determine the flow rate based on the ratio of the valve’s pressure-reducing ratio to the critical pressure ratio.

3. Selection of Pressure Reducing Valves:

1) Bellows-type pressure reducing valves (direct-acting) feature a flat diaphragm or bellows. They have an independent structure and do not require the installation of external sensing lines downstream. With a wide adjustment range, they are used in steam pipelines with operating temperatures ≤200°C. They are particularly suitable for heating systems that reduce pressure to low-pressure steam and are the smallest and most economical of the three types of steam pressure reducing valves.

2) Piston-type pressure-reducing valves offer reliable operation, low maintenance requirements, and a wide pressure-reduction range. For the same pipe diameter, they provide higher capacity and

greater accuracy (±5%). Like direct-acting pressure-reducing valves, they do not require external sensing lines. They are suitable for steam lines with higher

temperatures and pressures.

3) Diaphragm-type pressure-reducing valves have a higher capacity than internal-guide piston-type valves for the same pipe diameter. Additionally, because they are equipped with

downstream sensing lines, the diaphragms are more sensitive to pressure changes, achieving an accuracy of ±1%.

4) In situations where indoor steam supply pressure requirements are not stringent—that is, when the heat load is low and the radiators have high pressure resistance—

shut-off valves and pressure-regulating plates can be used for pressure reduction. The disadvantage is that they cannot adjust the required pressure downstream in response to fluctuations in the upstream pressure.

5) Water supply pressure-reducing valves feature a simple structure, compact size, stable performance, and convenient adjustment, making them suitable for cold and hot

water supply piping systems in high-rise buildings.

4. Considerations for designing pressure-reducing valves:

1) Piston-type pressure-reducing valves are generally recommended. The pressure after reduction should not be less than 0.10 MPa. If it needs to

reducing the pressure to below 0.07 MPa, a bellows-type pressure-reducing valve or a globe valve should be installed for secondary pressure reduction.

When the pressure ratio before and after reduction exceeds 5 to 7, two devices should be connected in series. If the steam pressure pz downstream of the valve is low, it is generally advisable

to use two-stage pressure reduction to minimize noise and vibration during operation and ensure safety and reliability. When thermal load fluctuations are frequent and severe,

the distance between the first- and second-stage pressure-reducing valves should be maximized to ensure stable operation of the first-stage valve.

2) During design, in addition to selecting the model and specifications, the pressure differential before and after the pressure-reducing valve and the opening

pressure of the safety valve should be specified to enable the manufacturer to properly configure the spring.

3) The selection range for the pressure differential △p across the pressure reducing valve should be: greater than 0.15 MPa for piston-type pressure reducing valves; and 0.05 MPa < △p < 0.6 MPa for bellows-type

pressure reducing valves.

4) When the pressure differential is 0.1 to 0.2 MPa, two globe valves can be installed in series to achieve pressure reduction.

5) Pressure reducing valves are directional; care must be taken during installation to ensure they are not installed in the wrong direction, and they should be installed vertically on horizontal

piping. For pressure reducing valves equipped with equalizing pipes, the equalizing pipe should be connected to the low-pressure side of the pipeline.

6) Flanged globe valves must be used for all pressure reducing valve installations. Low-pressure globe valves may be used for the low-pressure section, and the bypass pipe may be installed either vertically or

horizontally, depending on site conditions.