By Admin on Mon 09 October 2017 in Technical Information & Calculators
The flow of a fluid through any a valve (or any pipe fitting) is dictated by a number of factors:
1. The difference between the inlet pressure and the outlet pressure (otherwise known as the pressure drop or delta p or dp).
2. The diameter and length of pipe work on the inlet and outlet of the valve.
3. If the fluid is a liquid its specific gravity or if it’s a gas its relative density.
For further information see our Flow Calculation - (Kv) article.
However to make this easier and save you from having to do the maths we have created the Beta Valve flow rate calculators split into three media groups - liquid, air and gases.
Each group has three calculators that use the appropriate calculations for that media type:
- Calculating flow through a valve
Calculating the required Kv for a valve to give the required flow.
- Calculating the pressure drop for a valve
Using the Calculator
To use these calculators some information must be known.
1. The media (water, air, nitrogen etc.)
2. The inlet pressure.
3. The required flow.
Eg. Mains pressure water converts to 4 -6 bar (10 bar max), 2 meters head of water = 0.2 bar, a bucket filling in a minute is 9-10 litres per minute = 0.6 cubic meters per hour.
The pressure drop is tricky, if the valve is being used to control mains water filling a tank and is simply discharging into the tank through a very short (or no) outlet pipe then at the outlet of the valve the water will be at zero pressure - although it might have lots of velocity) all the pressure from the inlet is being “lost” across the valve.
If however the valve has a complex system of pipework, with elbows and/or spray nozzles being used these will affect the flow - in this case unless the customer has a pressure gauge or sensor in the system just after the valve then it’s very difficult to accurately assess the actual pressure drop across the valve. In this case assume that 10% of the inlet pressure is being lost.
Here is a guide to the specific gravity and relative density for various common liquids and gases.
These calculators have been produced with ACL valves in mind so uses m3/hr as the units of flow rate.
To convert to m3/hr to litres/minute multiply by 0.278
To convert l/m to m3/hr divide by 0.278
Choose the appropriate calculator and fill in the missing information and the answer will be calculated by the spreadsheet.
Gases and Air
The pressure used for gas and air calculations is absolute pressure.
At sea level we are exposed to 1 bar atmospheric pressure, yet if you take a pressure gauge off the shelf it will say 0 bar. 0 bar represents gauge pressure. Most pressure measurements in industry are gauge pressure unless otherwise noted. Add 1 bar to gauge pressure to give absolute pressure.
Example: a compressor supplies compressed air at 6 bar - this will be 6 bar gauge pressure, 7 bar absolute pressure.
Because of manufacturing variations in valves calculating flow like this is only accurate to + or - 10%.