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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Pelton Wheel flowmeters

Litre Meter manufacture and distribute an enviable range of flowmeters. From the low flow robustness of the VFF positive displacement meter to the precision of the Tricor Coriolis range, Litre Meter have a solution to your tricky measurement application.  Call our engineers now to receive the best advice on meter selection and application.

LM & MM Pelton Wheel

LMX Pelton Wheel
Stainless Steel Pelton Wheel LMX Flow Meter

The LMX series, pictured, was designed from the outset to meet two simple parameters: a pressure rating of 100 bar coupled with a temperature rating of 100°C. End couplings are either ½”NPT or BSP with built-in straight lengths of pipe. As a bonus, the minimum fluid temperature can be -50°C and there are just 3 wetted materials. With 316 stainless steel, PTFE and sapphire in contact with the fluid there are few applications that it can’t handle. Flow rate abilities are selected by different internal jets enabling the same size body to measure from 0.004 l/min up to 65 l/min in just a few sizes.

Applications are numerous. The Pelton Wheel was originally developed with petrol and water in mind.  These are both low viscosity fluids and are measured regularly, often at low flow rates. The smallest range (LM003) is designed to measure from 4 millilitres per minute up to 60 ml/min. As the jet size increases the rangeability also increases. The LM05, for example, 0.02 to 1.3 l/min and the LM220 is a magnificent 0.1 to 28 l/min.

These wide ranges can be attributed to 3 significant design factors:

  • Wide bladed pelton wheel design for maximum impulse
  • Sapphire bearings for minimal friction
  • A no-drag sensor to enable lowest flows

With over 44 years’ experience in these meters we have optimised the bearing and sensor design for long life and high efficiency with remarkable linearity.

Extending the flowmeters calibrated range – an expert view

It’s not an uncommon request.  When the enquiry comes in the client thinks the required range will be 1 to 10 but, once installed, it’s clear that he should have stated 2 to 20.  Then, the question is: what do we do?

First: it’s unlikely that the range can be extended beyond the meter maximum rated flow rate.  Some flowmeter principles can cope with excessive flow rates, probably at the expense of pressure drop, but most can’t.

Second: Consider the magnitude of change and the expectation of accuracy. If it’s a change from 1 to 10 to 1 to 11 with a 5% accuracy requirement when the maximum rate is 12 then that’s an easy one – check with the factory on how the range can be changed within the instrumentation but the range extension will be OK. On the other hand, if it’s a ±0.2% meter then it’s unlikely that any range extension will be within that value without a return to the factory for recalibration.

Here’s an example:

The client had purchased an LF03 VFF positive displacement meter for the measurement and control of corrosion inhibitor.  The viscosity was 55cP and, although the meter is capable of 18 litres per hour, had specified an operational range of 0.2 to 2.3 l/h which we calibrated over.

A year later we had a request for a range change – could they up the calibration range to 5.6 l/hr? Of course, yes. Could we provide a statement to this?  See below:

VFF Flowmeter Extended Range Accuracy – 50cP viscosity

The original calibration for meter VFF5112 was up to 2.3 l/hr on 55cP. Litre Meter have analysed the last 17 LF03s calibrated at or around 50cP and can confirm that re-ranging to 5.6 l/hr will have only a minor effect to system accuracy.

VFF Analysis:

It can be seen from the aggregated performance curves above that extending the flow rate above 2.3 l/hr up to 7 l/hr produces little change in the meter linearity. We would suggest that, in the absence of any higher flow rate information above 2.3 litre per hour, that the meter is unlikely to be outside of ±2% of the 2.3 l/hr pulses per litre value up to 7 litres per hour. Increased confidence and accuracy can be obtained by recalibration.

Linearisation:

Litre Meter produce a document LM0688 “Technical Description – Linearisation” that explains the linearization process and the flow rate versus pulses per litre table. Also here.

Reverse flow measurement – an expert view

Most flowmeters are setup for forward flow measurement. That is, they have a preferred direction for operation and that is adopted by the manufacturer/designer and advised to the customer.

Some flowmeters are symmetrical in the forward and reverse direction and will work in the reverse direction, too. Some are symmetrical and may not function or function well, due to meter design or principle, in reverse.

Finally, some meters may detect that the flow is in reverse and, better still, measure in either direction to the same accuracy.

We use the term flowmeter generically. When discussing flow direction and measurement we should consider the instrumentation as well as the flow sensor itself.

Distinctions:

Type A – not designed for Reverse flow, may cause damage:
Type B – can accept reverse flow, no detection
Type C – can accept reverse flow, detects direction of flow
Type D – Can accept reverse flow, measures accurately but doesn’t output direction
Type E – Accepts reverse flow and provides flow velocity and direction

B, C, D, E may need special instrumentation to extract the desired information.  The type designation just helps us understand the designs – it isn’t used outside of this article.

Flowmeter element Type
Orifice plate B, C, D or E
Wedge B, C, D or E
Venturi tube B, C, D or E
Flow Nozzle B or C
Pitot tube B
Elbow meter B, C, D or E
Target meter B or C
VA A or E (E with a special meter)
Positive Displacement A, B, C, D or E depends on design and sensing
Turbine A, B, C, D or E depends on design and sensing
Pelton A, B, C, D or E depends on design and sensing
Vortex A or B
Electromagnetic B, C, D or E – most units would be E
Ultrasonic(Doppler) B, C, D or E – most units would be E
Ultrasonic(Time-of-travel) B, C, D or E – most units would be E
Mass Coriolis B, C, D or E – most units would be E
Thermal Mass Insertion B
Thermal Mass Capillary B
Weir A
Flume B

 

Litre Meter flowmeters

Pelton Wheel

The LM range have a jet (apart from the LM220 and LM330). With a jet concentrating the flow onto the rotor, a reverse flow is very inefficient and the rate of rotation is much reduced for the same flow. The 220 and 330 are broadly symmetrical in some models and have different pipe layouts in most versions. These have never been fitted with technology to provide direction.

The same can be said of the larger, orifice plate based, MM meter. The inlet and outlet holes to the pelton wheel chamber are much different in size, so function poorly in reverse. A sole MM was manufactured with two pelton wheels and two sensors facing in different directions. By comparing the magnitude of the signals it was simple to tell which direction was active.

VFF

All VFF (rotary piston positive displacement) meters are perfectly symmetrical in design with rotors able to rotate clockwise or anticlockwise. There are small differences in machining so there are small differences in meter performance forward and reverse. There is a prescribed forward direction (purely for consistency) but the client can select the other direction as forward.

With a standard sensor the output is the same whether the flow is forward or reverse – just a series of pulses. When two sensors are fitted then the direction and magnitude of flow can be determined if the right instrumentation is used.

There are two suitable instruments used by Litre Meter and at least one system used by clients with varying degrees of sophistication. Sometimes two sensors are fitted for redundancy purposes. The instrument monitors one sensor. After a certain time period, if there isn’t a pulse attention is switched to the other sensor. The period is set to be a few seconds longer than the frequency for lowest flow achievable or the clients lowest expected flow.

Litre Meter use two sensor setups both based on reed switch sensing of the magnet in the VFF rotor. Litre Meter are developing a 3-D magnetometer based field sensor that can determine the position of the rotor in the chamber for finer pulse output.

If reed A switches before reed B then direction is forward. If B before A then direction is reverse.

The two reed switch setups are similar in concept but packaged differently. The original reed switch is situated in a sensor hole. When two reeds are used there are two parallel holes generally situated along the radius of gyration of the magnet. They are spaced to produce a clear lead or lag depending on rotor direction. The Fluidwell F115 is designed to interpret the lead/lag to produce a display with directionality.

With the introduction in 2015 of the CIFM versions of the VFF and the Litre Meter FlowPod the sensor was repackaged, with two reeds as standard, in an M8 stainless sensor body. Only one sensor hole is required as the reeds are side by side. The F115 and FlowPod can both interpret the CIFM sensor output.

F115

Fluidwell manufacture a wide range of instrumentation which Litre Meter have used since 2002. The F115 version is specifically designed for directionality. It does not have linearisation.

Description

The flow rate / totalizer model F115-P is a microprocessor driven instrument designed to show the flow rate, the total and the accumulated total. This model is able to detect the flow direction and to show a positive or negative flow rate, the totals for both directions and the cumulative totals.
This product has been designed with a focus on:

  1. ultra-low power consumption to allow long-life battery powered applications (type PB/PC),
  2. intrinsic safety for use in hazardous applications (type XI);
  3. several mounting possibilities with aluminum or GRP enclosures for harsh industrial surroundings;
  4. ability to process all types of flowmeter signals;
  5. transmitting possibilities with analog / pulse and communication outputs.
Flowmeter input

Two sensors with a phase difference of 90 or 270 degrees, can be connected to the F115-P.

Standard outputs
  1. Pulse output to transmit a pulse that represents a totalized quantity as programmed.
  2. Negative / positive pulse output indication – i.e. a flag.
  3. Linear 4-20mA analog output to represent the actual flow rate as programmed. The 4-20mA signal limits can be tuned.

FlowPod

Description

The FlowPod was designed from the outset with the CIFM sensor which is fitted with two closely positioned reed switches in one M8 stainless steel package. They are positioned in the flowmeter to provide a two separate pulses along the path of the spinning rotor. They are fairly close together such that there is a distinct time difference between reed A and B depending on direction.

In most installations the second reed is for redundancy purposes. The FlowPod monitors reed A. After a certain time period, if there isn’t a pulse, attention is switched to reed B. The period is set to be a few seconds longer than the frequency for lowest flow achievable or the lowest expected flow.

For directionality the FlowPod monitors reed A and B and interprets lead and lag to determine flow direction. Within the software forward direction can be set as ‘A before B’ or vice versa. Redundancy is still offered, although, of course, without direction.

Linearisation is standard on the FlowPod. The curve of flow rate versus frequency is similar in forward and reverse.

 

Measuring Sodium Hypochlorite in Hazardous Areas

Sodium Hypochlorite

Sodium hypochlorite is a green/yellow liquid with the characteristic smell of chlorine. It was first used as a bleaching agent and was then discovered to be effective in controlling wound infections. Subsequently, it is most commonly known as household bleach. The solution exhibits broad spectrum anti‐microbial activity and is widely used in healthcare facilities in a variety of settings. It is usually diluted in water depending on its intended use. Sign up for FlowSight, the Litre Meter newsletter.
In the chemical injection arena, it is common to inject sodium hypochlorite into sea water. Sea water can contain dissolved oxygen, bacteria and solids. These can affect an oil reservoirs life. Hypo is used as a bactericide whilst filters take care of the solids. Hypo is aggressive before it is diluted in the sea water and therefore requires some specialized devices in terms of wetted materials. Litre Meter have been manufacturing flowmeters since 1975.
We’ve always concentrated on the harder margins of metering typically at low flows and/or at high pressure. For this application note Litre Meter illustrate two solutions to this application based on <20 % solution. Download brochure.

Sodium Hypochlorite Flowmeters ‐ Applications and Rates ‐ VFF

The VFF has successfully metered fluids such as oils, hydraulic fluids, corrosion / wax / demulsifier / pour point dispenser /scale / hydrate inhibitors, biocides, oxygen scavengers, etc. for over 30 years. Meter bodies are produced in a variety of high grade materials which offer good chemical and environmental resistance. For sodium hypochlorite, Litre Meter recommend Titanium for the body and chamber with carbon graphite for the actual rotary piston. This ensures maximum compatibility, life and accurate response. The magnet is either encapsulated in titanium or PTFE.

VFF Flowmeter Sizes and Connections.

Applications for flow‐rates as low as 0.5 litres per hour have been supplied. Normal minimum flow rates depend on operating viscosity. In this case, viscosity is assumed to be between 1 and 2.5cP. Using the smallest VFF with carbon graphite rotor (LF15) and calibrating on water, which has a lower viscosity than NaOCl, a range of 0.5 to 40 L/hr is achieved. The meters range in size from the smallest titanium body, LF15 – 40 L/hr, to the largest V270 ‐ 270 L/min max. Higher flow‐rate meters are available to special order. The table at the end of this article assists in the selection of the best technology.

Sodium Hypochlorite Flowmeters ‐ Applications and Rates ‐ Pelton Wheel

Litre Meter started manufacturing the Pelton Wheel turbine in 1975. These usually had some stainless steel components together with a plastic rotor, elastomer seals and sapphire bearings. All plastic versions soon followed, including all Polypropylene, all PFA, all PVC and all PVDF. The other wetted parts are still sapphire with a suitable elastomer such as FKM or FFKM for the single O ring seal. The normal specification for Sodium Hypochlorite compatible Pelton Wheel flow meters is now PVC for the main body and cap with PVC or titanium internals, sapphire bearings, an FKM O‐ring and PFA rotor.

Pelton Wheel Flowmeter for Sodium Hypochlorite

The Pelton Wheel is an economical device with low pressure ratings and needs to have relatively steady state non‐pulsing flows.
The table at the end of this article assists in the selection of the best technology.

Compatible Materials

Due to the nature of Sodium Hypochlorite only a select group of tested materials is recommended by Litre Meter. We tailor our meters using three key materials, developed over 30 years of measuring Sodium Hypochlorite:

PVC, Hastelloy and titanium
The PVC design can be used up to 15 bar pressure maximum. Hastelloy (UNS N10276) up to 1035 bar. For the ultimate select titanium (UNS R50400) designed for 1380 bar (20,000psi, 20 ksi)

These material make up the body and the cap of the meter. The seals between the meter body and cap are normally FKM. Other seal materials include FFKM and PTFE. All seals within the meter are fully compatible with Sodium Hypochlorite.

Flow ranges and references

All Litre Meter manufactured flowmeters are custom calibrated across the customer specified minimum to maximum flow conditions and working viscosity. The minimum flow rates achievable are dependent on fluid viscosity. With sodium hypochlorite, in most normal concentrations, water is used as the calibration medium as this proves to be the best for accurate calibration representation. The table below assists in selecting which technology is preferred.
Normal engineering materials like 304 and 316 stainless steel, aluminium, brass and steel are unsuitable due to the aggressive nature of the free chlorine in the Sodium Hypochlorite. Plastics such as PVC and PTFE are suitable together with Hastelloy C and purer grades of Titanium.

Comparison table:
Table showing selection criteria for Sodium Hypochlorite meters in two different flow technologies.

Flowmeters for Sodium Hypochlorite – Hazardous Area, too

Sodium hypochlorite

Sodium hypochlorite is a green/yellow liquid with the characteristic smell of chlorine. It was first used as a bleaching agent and was then discovered to be effective in controlling wound infections. Subsequently, it is most commonly known as household bleach. The solution exhibits broad spectrum anti‐microbial activity and is widely used in healthcare facilities in a variety of settings. It is usually diluted in water depending on its intended use.
In the chemical injection arena, it is common to inject sodium hypochlorite into sea water. Sea water can contain dissolved oxygen, bacteria and solids. These can affect an oil reservoirs life. Hypo is used as a bactericide whilst filters take care of the solids. Hypo is aggressive before it is diluted in the sea water and therefore requires some specialized devices in terms of wetted materials.
Litre Meter have been manufacturing flowmeters since 1975.
We’ve always concentrated on the harder margins of metering typically at low flows and/or at high pressure. For this application note Litre Meter illustrate two solutions to this application based on <20 % solution.

Sodium Hypochlorite Flowmeters ‐ Applications and Rates ‐ VFF

The VFF has successfully metered fluids such as oils, hydraulic fluids, corrosion / wax / demulsifier / pour point dispenser /scale / hydrate inhibitors, biocides, oxygen scavengers, etc. for over 30 years. Meter bodies are produced in a variety of high grade materials which offer good chemical and environmental resistance. For sodium hypochlorite, Litre Meter recommend Titanium for the body and chamber with carbon graphite for the actual rotary piston. This ensures maximum compatibility, life and accurate response. The magnet is either encapsulated in titanium or PTFE.
Applications for flow‐rates as low as 0.5 litres per hour have been supplied. Normal minimum flow rates depend on operating viscosity. In this case, viscosity is assumed to be between 1 and 2.5cP. Using the smallest VFF with carbon graphite rotor (LF15) and calibrating on water, which has a lower viscosity than NaOCl, a range of 0.5 to 40 L/hr is achieved.
The meters range in size from the smallest titanium body, LF15 – 40 L/hr, to the largest V270 ‐ 270 L/min max. Higher flow‐rate meters are available to special order. The table on the last page assists in the selection of the best technology.

Sodium Hypochlorite Flowmeters ‐ Applications and Rates ‐ Pelton Wheel

Pelton Wheel Flowmeter for Sodium Hypochlorite

Litre Meter started manufacturing the Pelton Wheel turbine in 1975. These usually had some stainless steel components together with a plastic rotor, elastomer seals and sapphire bearings. All plastic versions soon followed, including all Polypropylene, all PFA, all PVC and all PVDF. The other wetted parts are still sapphire with a suitable elastomer such as FKM or FFKM for the single O ring seal.
The normal specification for Sodium Hypochlorite compatible Pelton Wheel flow meters is now PVC for the main body and cap with PVC or titanium internals, sapphire bearings, an FKM O‐ring and PFA rotor.
The Pelton Wheel is an economical device with low pressure ratings and needs to have relatively steady state non‐pulsing flows.
The table on the last page assists in the selection of the best technology.

Compatible Materials

Due to the nature of Sodium Hypochlorite only a select group of tested materials is recommended by Litre Meter. We tailor our meters using three key materials, developed over 30 years of measuring Sodium Hypochlorite:

These material make up the body and the cap of the meter. The seals between the meter body and cap are normally FKM. Other seal materials include FFKM and PTFE. All Seals within the meter are fully compatible with Sodium Hypochlorite.

Flow ranges and references

All Litre Meter manufactured flowmeters are custom calibrated across the customer specified minimum to maximum flow conditions and working viscosity. The minimum flow rates achievable are dependent on fluid viscosity. With sodium hypochlorite, in most normal concentrations, water is used as the calibration medium as this proves to be the best for accurate calibration representation. The table below assists in selecting which technology is preferred.
Normal engineering materials like 304 and 316 stainless steel, aluminium, brass and steel are unsuitable due to the aggressive nature of the free chlorine in the Sodium Hypochlorite. Plastics such as PVC and PTFE are suitable together with Hastelloy C and purer grades of Titanium.

Comparison Table:

Table showing selection criteria for Sodium Hypochlorite meters in two different flow technologies.

Litre Meter can provide optimum solutions for a wide range of flow rates of Sodium Hypochlorite. Using a variety of materials, a flowmeter can be constructed that handles any specific concentration of NaOCl and provide a display and/or output for measurement and control. For references etc please download our brochure.

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