General information Useful calculation data
7
Local regulations may restrict the use of this product to below the conditions quoted. In the interests of development and improvement of the product, we reserve the right to change the specification without notice. © Copyright 2019
TI-GCM-08 CM Issue 2
Saturated Steam Sizing Chart
Let:
= Mass flow in kg/h P 1 = Upstream pressure in bar a P 2 = Downstream pressure in bar a K v = Valve flow coefficient.
= Pressure drop ratio = P 1 - P 2 P 1 Note: To convert gauge pressure to absolute pressure, add 1, i.e. 10 bar g = 11 bar a.
The chart overleaf shows that with a given upstream pressure P 1 and with a pressure drop across the valve more than is needed to give critical flow conditions, or > 0.42, the steam flowrate is directly proportional to the K v of the valve. Conversely, with a given K v , the flowrate is directly proportional to the upstream pressure P 1 . So for critical flow, we have:- = C x K v P 1 and in the units shown, C = 12 (Constant). Thus: = 12 K v P 1 With a smaller pressure drop, the flow is reduced until it becomes zero, at zero pressure drop. Many formulas are in current use to predict the relationship between flowrate and the pressure drop ratio under these conditions. One empirical formula which gives results very close indeed to the British Standard method, but simplifies the calculation, is:- = 12 K v P 1 1 - 5.67 (0.42 - ) ² If this formula is used when P 2 is below the value which gives critical flow, then the term within the bracket (0.42 - ) becomes less than zero. It is then taken as zero, and the function within the square root sign becomes 1.
7.5 9
Example 1: How to find K v value for a critical flow application.
page 2
How to use the chart
Example 2: How to find the K v value for a non-critical flow application.
page 3
Example 3: How to find the pressure drop across a valve with a known K v .
page 4
Saturated steam sizing chart
page 5
11.5.6
Page 1 of 5
Powered by FlippingBook