Also known as a radial turbine, the highly efficient Pelton Wheel flow meter has some major advantages, with a range of flow rates.
The LM series is for lower flows and have some spectacularly wide flow rate range capabilities. The MM series is the larger series, continuing at ½” and above. Pelton Wheel flow meters are ideal for low viscosity liquids such as water and low flows. The smaller flow ranges are handled by the LM series whilst for 1/2″ pipe sizes or 30 l/min and above the MM series is available.
Both series use the same rotor and ring assembly with the MM series being mounted in a bypass chamber across a custom orifice plate.
What is a Pelton Wheel Flow Meter?
Litre Meter have manufactured the LM GN, LM and MM range of Pelton Wheel turbine flowmeters since 1975.
Pelton Wheel flow meters are ideal for low viscosity liquids and low flows. The smaller flow ranges are handled by the LM series whilst for 1/2″ pipe sizes or 30 l/min and above the MM series is available. The original design, GN, has two hose connectors and a slightly limited range of sizes. Even so, flows from 0.01 to 28 l/min can be handled. A wider selection is in the LMX range which has the LM003 at the low end (0.004 to 0.060 l/min/ 4-60 ml/min), some intermediate sizes and finishes up at the 280:1 LM220 – (from 0.1 to 28 l/min). The LMX has 1/2″ BSP or NPT male connections including a straight length to take care of odd flow profiles giving them an overall length of 180mm and a pressure rating of 100bar. A 230bar version with an FPM seal rather than PTFE is optional.
The MM Pelton Wheel design is notable in that it uses exactly the same rotor and ring assembly as the smaller LM range. It achieves this by being mounted in a bypass chamber across a custom orifice plate. The rotor movement is then proportional to the total flow through the meter. The threaded or piped sizes cover flow rates up to 220 l/min. Above that rate the design switches to a very compact wafer design. This gives a wide rangeability, typically 50:1 for the MM orifice/ by-pass meter. The MM12.5 size has 1/2″ connections just like the LMX.
The LMX Pelton Wheel Series
Also known as a radial turbine the highly efficient Pelton Wheel meter has some major advantages. The very large blade area compared with the flow inlet port size produces an exceptionally wide range flowmeter which can measure very low flows. The flow through the inlet of the meter is accurately directed onto the rotor which rotates at a speed in linear proportion to the flow rate. A small sensing coil detects the ferrites mounted in the rotor blade tips as they pass. No drag is imposed on the rotor which assists in the measurement of extremely low flows. Sapphire bearings provide a very low friction mechanically-robust bearing with long life characteristics. Turndown can be as high as 280:1.
Each size Pelton Wheel flow meter has its flow rate range controlled by jet size. For example, the LM24 has a 2.4mm diameter jet and a flow range of 0.03 to 4.3 litres per minute.
The LMX series are in line. The stainless steel units incorporate inlet and outlet pipes.
The MMX Pelton Wheel Series
Each size Pelton Wheel flow meter has its flow rate range controlled by the connection and orifice size. For example, the MM20 has 3/4″ connections and a flow range of 2 to 130 litres per minute. The ring assembly with rotor is the same size irrespective of flow rate and connection size.
All MM flow meters are custom calibrated across the customer specified minimum to maximum flow conditions on water. The minimum flow rates achievable are dependent on fluid viscosity; the flow minima below are for water.
|Flow Ranges l/min (LMX / MMX)||
0.006 - 0.100 up to 0.1 - 28 / 1 to 65 up to 10 - 500
±2% of actual reading for the top 90% of range
|Pressure Rating (LMX/MMX)||
30 bar - 100 bar / 40 to 100 bar
|Temperature Rating (LMX/MMX)||
100° C / ‐40 to +100°C
|Viscosity Range (LMX/MMX)||
Up to 10 cPs; ring factory if higher
±0.2% reading over top 90% of range