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Calculation of Pressure Regulators for Steam |
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Selecting a suitable valve
Our selection tables and data sheets contain all the technical data needed to select MANKENBERG valves.
The Kvs-value of the selected valve should be equal to the calculated Kv-value plus the required allowance. Most valves
operate most efficiently within 10 to 70 % of their Kvs-values; small non-balanced valves such as our pressure reducers
types 152, 505 and 701, will operate satisfactorily even at minimum flow rates.
You should select a setting range which places the required control pressure at the top end. If, for instance, the pressure to be controlled
is 2.3 bar, you should select the 0.8-2.5 bar range rather than the 2-5 bar range, as with the latter the control errors would be considerably
greater. If in special cases the standard setting range is not wide enough, a lower setting range may be selected provided the valve operates at
low capacity and the control accuracy is of minor importance. Under such conditions, for instance, a pressure reducer featuring a setting range
of 0.8-2.5 bar may still operate satisfactorily at 0.5 bar.
You should select the materials in accordance with the operating requirements by using the material resistance table.
Let us return to our example:
Based on the operating data we had calculated a minimum Kvs-value of 16.8 m³/h. According to our selection table several valve types meet this requirement.
We select pressure reducer type 652, DN 50, Kvs-value 18 m³/h, setting range 2-5 bar. In its standard version this valve is manufactured from materials
which are suitable for the application.
Additional features are high control accuracy, low weight, good surface quality and a price which is remarkably low for a stainless steel valve.
Here is another example:
We are looking for a pressure reducing valve capable of reducing the pressure of 8 t/h of 460°C superheated steam from 100 bar to 20 bar for the
purpose of soot blowing.
| The pressure drop is supercritical because |
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, namely 80 > |
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As we do not know the specific volume at the moment, we calculate
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= 9,33 m³/h |
To the Kv-value calculated from the operating data we add an allowance of 30 % and thus obtain the minimum Kvs-value which the
valve to be selected should have.
Kvs-value = 1,3 x Kv-value = 1,3 x 9,33 = 12,1 m³/h
Under operating conditions the volume flow rates are
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m³/h |
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m³/h |
and accordingly, given a maximum permitted flow velocity of 50 m/s, the minimum pipeline diameters are
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= 43,3 mm |
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= 94,5 mm |
Consequently we would recommend a DN 50 pipeline upstream and a DN 100 pipeline downstream of the valve.
Using the calculated data and taking into account the special operating conditions, we select the twin seat
pressure reducer type 401 ZK, DN 50/80, Kvs-value 16 m³/h, setting range 15-25 bar, complete with adjustable
damper unit and armoured seats and cones - a design which has proved reliable in many soot blowing systems.
download the PDF-file:  Calculation of pressure regulators / PDF (156 kb)
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