Rotameter

• Variable area flow meter and rotameter
• Simple reliable visual indication of flow rate
• No power required, can be used in hazadous zones
• Compact installation as no straight pipe is required at inlet or outlet
• Fit directly to elbows for neat & easy panel mounting
• Low cost
• Linear scale
• Robust PVC & ABS & acrylic, corrosion resistant materials
• Negligble & constant pressure loss
• Pipe diameters from DN15 to DN65 with union ends, larger diameters with flanges
• Accuracy ±4%
• Maximum pressure 600KPa
• Temperature range 0-60°C
• Optional switches for low and high flow alarms
• Union ends for simple radial removal if cleaning is ever required
• Flanged version for pipe sizes up to 6” (DN150)
• Mercon meters have solvent cement sockets sized to suit Australian pipe
• Other connections are available
• BSP threaded connections
• Flanges. Test
• Metric solvent sockets
• Models for flow rates from 50L/H to 60M³/H, see dimensions & specifications
• EPDM seals are standard, FPM (Viton) are optional
• Short tube meters have a stainless steel leader rod to stabilise the indicator, for corrosive applications specify a PTFE leader

Also known as a rotameter, these simple indicators give a repeatable measurement of flow rate for clear liquids & low-pressure air or gas. They consist of an indicator in a transparent tapered tube, as the flow rate increases the indicator rises in the tube, the top of the indicator aligns with a linear scale on the body so the flow rate can be read directly from the scale.

This type of meter is always installed in a vertical section of pipe with the fluid flow upwards. There are no requirements for straight runs of pipe at the inlet or outlet of the meter because of the operating principle of the instrument. Stable flow will assist in the convenience of reading the flowrate & extend the working life of the device.

There are 2 upward forces on the float, the drag force from flowing liquid and the buoyancy force due to the difference in density between liquid and the float.

There is a downward force due to the weight of the float. In practice the only variable is the drag force, so as the flow rate increases the float rises in the tapered tube increasing the area of the annulus at the position of the float. Hence the float reaches a point of equilibrium when this increase in area creates a balance of the forces on the float.

These names are interchangeable, variable area flow meter best describes the operating principle of the device. Rotameter is the registered brand name of a prominent manufacturer of these instruments.

They are simple devices that do not require any electrical power, so they are cheap to install in remote or hazardous areas. They are optical so the operator can see if the process is contaminated by solids or entrained air. They do not require straight lengths of pipe at the inlet or outlet, so the installation is compact and economical. They have a linear scale; they are reasonably accurate and give very repeatable results. They can be fitted with electrical switches to give a remote indication of high or low flow.

Large rotating equipment often needs auxiliary services such as coolant water, lubricating oils, gland seal water. These meters are ideal in conjunction with a control valve, an operator can adjust the flow and immediately observe the effect. Chemical dosing often requires the mixing of separate streams of liquids at a specific flow rates. Sampling equipment such as pH & ORP sensors require a consistent and steady flow. Much industrial equipment requires purge air for safety considerations and this is another useful application for VAFs.

• Analyser sample flows
• Bearing cooling water flows
• Gland seal flows
• Flows to pH and ORP and similar sensors
• Alternative models with polysulphone or polycarbonate tubes available for high temperature or high pressure applications
• Variable area flow meter dimensions
• Variable area flow meter dimensions & ranges
• Code example
• VAF-15B is a long tube 1/2″NB meter range 16-160L/H
• Flow alarm switches should be ordered as ALo or AHi or 2AHL
• VAF-15STB is a long tube 1/2″NB meter range 16-160L/H
• What is a variable area flow meter ?
• How should a variable area flow meter be installed?
• What is the working principle of the vatiable area flow meter?
• VAF principle of operation
• It is important that the manufacturer is aware of the density of the liquid for accurate calibration of flow rate
• What is the difference between a rotameter and a variable area flow meter?
• What are the advantages of a variable area flow meter?
• What applications use plastic bodied variable area flow meters?