Secondary pressure ranges higher than 1,6 MPa and lower than 0,05 MPa on request available.

Capacity Chart

Tables of calculation for steam
RE20 (REH20, REC20)
RE20L (REH20L, REC20L)

How to select the size of a PRV correctly?

Check the operating data:

• Inlet pressure p₁
• Requested downstream pressure p₂
• Requested steam flow

Check the requested steam flow in the capacity chart on page 15. Select the necessary size of the PRV. Table 1 shows the maximum available steam flow in kg/h at a given inlet pressure, if the ratio between the requested downstream pressure p₂ and the inlet pressure p₁ is lower than 0.577 (critical flow). Pay attention that the steam pressure is shown as bar_abs!

If the ratio between the downstream pressure p₂ and the inlet pressure p₁ is larger than 0.577 (non-critical flow), the available steam flow amount on the downstream side will be reduced. To get the maximum available downstream flow amount, the maximum steam flow from Table 1 must be multiplied with the calculation factor A. To get the Factor A see the Diagram 1.

Check if the requested steam flow matches the downstream side using Table 2 (page 16) for flows under 40 m/s. Choose the size based on barg pressure. If downstream piping is 1–2 sizes larger than the PRV inlet, you’re good. If the size difference is over 2, increase the PRV size. Keep the difference within 2 sizes!

Example of calculation

Operating data:

• p₁ = 9 barg = 10 bar_abs
  p₂ = 6 barg = 7 bar_abs
  Steam flow G = 1,100 kg/h

Search for the necessary size of the PRV in accordance with p₁.

• Table 1 shows 1,312 kg/h for size DN40 (1½”).
• bar_abs = 0.7 (i.e., larger than 0.577)
• Factor A acc. to Diagram 1 = 0.96
• Max. available steam flow G = 1,312 kg/h × 0.96 = 1,259 kg/h.

Steam flow in accordance with Table 2 at 6 barg = 1,720 kg/h for DN65.

Conclusion:
The PRV with an inlet size of DN40 and increase of the pipe size to DN65 at the downstream side will be suitable for a flow amount of 1,100 kg/h at the given pressures.

Capacity Chart
The Table 1 shows the maximum available steam flow amount of the pressure reducing valve at a given inlet pressure, if the ratio between the downstream pressure p₂ and the inlet pressure p₁ is lower than 0.577 (critical flow). Pay attention that the inlet steam pressure p₁ is shown as bar_abs.

Table 1

Capacity Chart
The Table 2 shows the maximum available downstream steam flow amount of the pressure reducing valve at the requested downstream pressure p₂. Pay attention that the steam pressure p₂ is shown as barg.

Table 2