Custom Pelton Wheel flowmeter designs

Litre Meter have manufactured pelton wheel flowmeters since 1975.  They are based on a light-weight, low inertia, plastic rotor spinning on jewelled bearings and monitored by a no-drag pick off.

The standard range covers many flow rates, materials, end connections and pressure ratings.  The wide rangeability and compactness lends their design to a multitude of applications.  Every now and then, customers request some interesting variations, for a variety of reasons.

Company A. Our oldest current client first bought meters from us in 1980. Their remit was an all stainless design with welded connections. Something compact was a benefit so Litre Meter varied the design of the then LM220-20bar. 1/4″NPT end connections were added and hundreds have been sold over the years.  Issues were found on some older units in high humidity locations so the meters were redesigned to meet EP455. Additionally, the redesign was an ideal opportunity to integrate some of the customers own modifications. The current version has an internal ‘divide by 10’ circuit to reduce the output frequency.  Meters are provided within a specific range of meter factors and have full immersion tests on a batch basis.

LM220 with 1/4″NPT connections, welded construction, wide flow range

Company B. This customer purchased hundreds of flowmeters for the measurement of  32% Caustic, 40% Nitric or 3% Peracetic Acid. The major material was 316SS whilst plastic wetted parts were either Polypropylene or PVDF; seals were FPM or EPDM both depending on the fluid. Unique modifications included in-line 1/2″ Table D flanged connections and a scaling feature enabling the output to be 10 pulses per litre.

Company C. In the automotive sector, one customer started customising the Pelton Wheel meter themselves.  They substituted the standard nylon flow body with stainless steel. Litre Meter stepped in and offered a slimline stainless steel body with metric OD pipe connections. Hundreds were subsequently ordered over two continents for fuel flow measurement.

Flowmeter M8
Development phase, with brass unions, later replaced with 316 stainless steel to match the rest of the construction.

Company D. Amine is used in the casting industry to set the sand in place prior to casting. Sand moulds are cheap and suit the casting process. The sand is bonded together with a chemical binder – in this case an amine. It is liquid through the flowmeter and turns to gas within the core. The customisation relates to 3 different aspects. Firstly, and perhaps most importantly, the ‘on’ time for the meter is very short, in the region of a few seconds. The meter has to ramp up very quickly, provide enough pulses to be useful and accurate. Secondly, the meter had to fit within an existing pipework configuration, This resulted in a unique configuration:

Unique Orientation
Pelton Wheel meter with welded pipes

Thirdly, because the amine is very low viscosity, calibration was changed to acetone rather than water.

Company E. The customer had purchased various custom pelton wheel meters over the years for progressively higher and higher specifications. Most were the LM220 which has an enormous flow range.  All were for aerospace applications measuring jet fuel or similar on-board an aircraft. The image below shows the latest one, carefully engineered to provide the best linearity within a very tight, odd-shaped, envelope.

Pelton Wheel
Custom Pelton Wheel for limited space, manifold connection

The testing regime involved simulating not just flight but also transport to the aircraft, by various means, and take-off under extremes of temperature.  This was as much a test of the flowmeter as it was for the laboratory.  The design incorporated a pressure sensor and a manifold connection for the customers valve plus a new sensing method.

 

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Six Degrees of customisation

Litre Meter supply a range of flow meters for Oil & Gas applications. They specialise in customising a range of flowmeters to meet specific customer requirements. A good example of this is flow meters for subsea use i.e. with the ability to work subsea and transmit a flow signal signal to the surface. The image (from 2011) shows another which uses many of the custom attributes of the VFF series of rotary piston positive displacement meter.

A 2011 VFF showing 5 degrees of customisation

There are six degrees of customisation:

  • Connections – in this meter Grayloc hubs were utilised
  • Materials – normally 316 but Duplex S32760 was specified
  • Flow Range – This series included 139 meters all with PVD coating, removable PBCs and special calibration ranges.
  • High Pressure – most were 1035 bar/15,000 psi/15ksi
  • Communication – these had HART 5. The current FlowPod versions offer HART 7
  • Subsea – The only missing degree…
A 2018 VFF Flowmeter showing the compactness of the FlowPod display. Same 5 degrees of customisation: High pressure, special connections, communication, low flow, flow range

PBC

The Pressure Balanced Chamber (PBC) is used to isolate the measuring element from the pressure vessel purpose of the VFF. This allowed optimised materials for the rotor and chamber – to give better flow range, for example, and simultaneously enabled the use of more exotic materials for the pressure vessel. Many more units have been constructed in duplex and super duplex which would have proved almost impossible to use for measurement surfaces (due to the tolerances of manufacture).

PVD

When Litre Meter separated the meter into two functions of measurement and pressure containment the use of coatings could be exploited. After careful selection and testing all of the VFF range are now supplied with PVD coating. This remarkable addition enables both higher and lower flow rates. For example, and it is the best example, the HF66 size was rated to 66 l/min maximum. Typically, without coating, the stainless steel rotor could measure down to 5 l/min on water. With the PVD coating the coefficient of friction is reduced and the minimum reduces to 12 l/hr, yes 12 litres per hour, and the added hardness enables over-range up to 130 l/min – subject to factory approval.

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