Do you have noisy steam or gas valves?

Article by Dr Hans D. Baumann, Ph.D., P.E.
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Having found the underlying algorithms based on fundamental laws of fluid mechanics and acoustics which enable the calculation of sound levels of compressible fluids emanating from control valves, and thereby simplifying the IEC Standard and improving accuracy, I thought that a similar method applying to gases might also be good. However this task proved to be quite difficult. After much time and effort I finely was able to compress over 40 equations of an IEC prediction standard into three graphs plus a few modifiers. I thought such a simplified graphical method might be a handy alternative to a computerized method. While this method,as exhibited, is valid for air, it could be modified for other gases as long as the specific gravity and sonic velocity are accounted for (see adjustments below).

The results are three graphs A, B, and C, which condense the equations of the underlying mathematics.

1) The first graph A shows sound levels as function of the given valve’s outlet pipe diameter(D) either in inches or in mm, and as function of the relative flow capacity (Cv / D2);D in inches, or Cv /(0.04 x d)2 if d is given in mm. The graph also incorporates the pipe’s transmission loss based on schedule 40 pipe (for schedule 80 see below). Note: Cv is based on actual process conditions.

2) The next step is to consult Graph B based on the absolute inlet pressure to the valve either in psia or in bar absolute. Find the appropriate dB(A) numbers corresponding to the valve inlet pressure and add it to the results from Graph A. Then proceed to Graph C.

3) In Graph C, the first step is to find the valve’s pressure ratio, where X = (P1 – P2 / P1), here P1 is the absolute inlet pressure and P2 the absolute outlet pressure. Multiply X by ten and find the corresponding 10X number on the bottom of the graph. Read up to the curve agreeing with the Fd numbers of your valve. Fd affects the diameter of the noise producing jet. Next read the corresponding dB(A) number on the left. (Use the “Tabulation of Fd – Factors” below for estimating purposes in case you don’t know your valve’s Fd number).

• If your pipe is schedule 80, add 4 db(A).
• If this is a rotary valve, add rw = 3 dB to the total. 

1. A = 7.3 dB(A) for 2” (50 mm) size and a Cv/D2 of 3.1 or, 12.5/(0.04 x 50)2 = 3.1 also for d in mm. 
2. B = 30.1 dB(A) for P1 of 72.5 psia (5 bara) 
3. C = 34 dB(A) based on 10X = 8 = 10x (P1–P2/P1) and Fd = 0.07

Subtract –4.2 for helium

Total estimated sound level per the graphs = 7.3 + 30.1 + 34 – 4.2 = 67.2 dB(A). Test results from Figure 5 of reference 1 = 69 dB at 1 m distance from the pipe and at a pressure ratio P1/P2 of 5. Offset: 1.8dB, see Figure 1. Figure 2 shows the test results for an 8” (200 mm) segmented ball valve installed in a 16” (400 mm) pipe; (D = 16”). Here are the data: P1 = variable (this is a blow-down test), P2 = 14.5 psia (1 bara). In example, P1 = 2.5 bara, Cv = 134, Fl = 0.6 and Fd = 1, rw = 3. Note, here A = 134 / 16”2 or 0.52. As the graph shows, there is reasonable agreement between test data and estimate except in very high pressure ratios. As an example, at P1 =2.5 bara, A = 14, B = 16.1, C = 51, rw = 3. Total: 14 + 16.1 + 51 + 3 = 84.1 dB(A) at 1 meter from pipe (test data at 10X = 10x(P1–P2/P1) of 6 = 89 dB(A)).

Note: This method is not applicable when a valve is installed in an enlarged outlet pipe when the valve’s outlet velocity into the expander exceeds 0.3 Mach. Valves without expanders are exempted from this rule (see Figure 1).

Adjustments for gases other than air can be calculated as follows:

Ng = 10 log(M_gas/28.9) + 20 log(Ci_gas/343) + 5 log (Gg_gas/1)

Legend: M_gas = molecular weight (kg/kgmol), Cig_gas = sonic speed of gas (m/s), Cg_gas = specific gravity of gas.

Examples: Ng for sat.steam: 1, natural gas: –4.5, oxygen: +0.3, helium: –4.2, Methane: –1(all in dB(A)).

• Inlet pressure 2.8 dB
• Density of gas 0.4 dB
• Pressure drop 1.4 dB
• FL factor 1 dB
• Fd factor0.8 dB
• Flow coefficient (Cv/Kv) 0.4 dB. 

The author extends his gratitude to Mr. John Roper for producing the fine graphs.

Dr. Baumann has kindly provided the algorithms for the convenience of readers who wish to use this method on their own computers.

A = 25 Log(D) – 10 + 20log(Cv/D2)

B = 35 log(P1) – 35 (Note, if P1 is in bara

use: 35 log(14.5 P1) – 35)

C = 60 – 32 log (10 /10X) + 20log (Fd)

LAe = A + B + C + G + rw in dB(A)

G = 1 for air; for other gases see above,

rw = 0.25 for globe valves, 0.5 for line-ofsight valves.

Example: D = 4 (100 mm) Cv/D2 3.15,

A = 7.4; P1 = 72.5 psia (5 bara), B = 30.1;

10X = 8 with Fd = 0.07, C = 33.7 dB(A)

Dr. Baumann, a former Vice President of Masoneilan and Fisher Controls created his own company, after serving as international consultant. He was named one of fifty most influential inventors and is credited with over 100 US patents. He has authored 170 publications and seven books, including the Control Valve Primer which is now in the fourth edition. His honours include being elected an Honorary Member of ISA and a Fellow Member of ASME.