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Calculation of Pressure Regulators for Liquids |
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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 502, 505, 506, 510, 762 and 765, 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 3.61 m³/h. According to our selection table several
valve types meet this requirement. In view of the properties of the fluid to be handled we select pressure reducer type 652, DN 25,
Kvs-value 6 m³/h, setting range 2-5 bar, spring cover with leakage line connection. In its standard version this valve is
manufactured from materials which are compatible with methanol. 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 overflow valve (back pressure regulator) capable of discharging 250 m³/h of drinking water into an open reservoir
at a pressure of 10 bar.
First we calculate the Kv-value corresponding to the operating data. Although the pressure drop ( p1 - p2 ) is 10 bar,
we shall use for our calculation a pressure drop of only 0.6 p1 [bara] = 6.6 bar because of the evaporation which occurs across
the valve seat. Thus:
Hence the Kvs-value of the valve should be at least 1.3 x 97.3 = 126.5 m³/h.
We select the pilot operated overflow valve type 824, DN 200, Kvs-value 180 m³/h, setting range 4-12 bar, - a relatively economical,
lightweight and very accurate control valve made from steel or better stainless steel.
Let us give another example:
We are looking for a CIP pressure reducing valve capable of reducing the pressure of demineralized water from 2-4 bar to 0.7 bar at a rate
of 1-3 l/min. The pipeline has a nominal diameter of 25 mm and Tri Clamp connection.
Based on the operating data we again calculate the Kv-value as follows:
Hence the Kvs-value of the valve should be at least 1.3 x 0.16 = 0.21 m³/h.
We select the pressure reducer type 152, DN 25, Kvs-value 3.5 m³/h, setting range 0.8-2.5 bar, an angled stainless steel valve which
can be polished. We have selected this valve, although its Kvs-value is relatively high and the required outlet pressure is outside
the specified setting range, because extensive bench testing has shown that this valve is ideal for the above-mentioned operating conditions.
We have used this example to demonstrate that in special cases valves can be used outside the parameter ranges specified in the catalogue provided
that the user has a good knowledge of the operating characteristics of the valve.
download the PDF-file:  Calculation of pressure regulators / PDF (156 kb)
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