Variable Area Flow Meters

Bye Pass Rotameter

Eureka make Byepass Rotameters are being used for variety of applications in the industry for several years. These are available for flow measurement in pipe size 1” & above. These can be used for clean non viscous liquids & variety of gases. Special models for corrosive fluids are also available. These flowmeters can be installed in horizontal as well as vertical piping systems. Three different designs are available based on the type of pressure tapping used.

Working Principle

A Byepass Rotameter is a differential pressure measurement type flowmeter.It consists of three components.

1. Main line Orifice Plate: An Orifice plate is installed in the main pipe line whose flow rate is to be measured. The plate can either be installed in between the flanges or a carrier ring assembly. This orifice plate creates a differential pressure due the restriction created to the main line flow. The differential pressure varies with the fluid flow in the main line. Based on the differential pressure, the flow through a pipe can be established using a mathematical equation.
2. Indicating Rotameter: This is a Glass/Metal tube inline rotameter which is installed in a byepass arrangement. A small range orifice is fixed at the inlet of this rotameter .The range orifice is designed to create the same differential pressure which is created by a main line orifice plate. With this arrangement the rotameter works as a manometer or a differential measuring device.
3. Byepass Piping: Byepass arrangement is used to divert a small portion of flow from the main line through an indicating rotameter. The flow at the upstream side of a main line orifice plate is connected at the inlet of the rotameter & outlet of the rotameter is connected to a downstream side of an orifice plate. The isolation valves are also provided in the byepass piping system for easy maintenance.
Eureka make Byepass Rotameters are offered by using three types of pressure tappings.

1. Corner Tapping: (Ref FIG.A) It is normally used for carrier ring type arrangement. The pressure taps are drilled through a carrier ring assembly. These taps open at the corner of an orifice plate mounted in between the carrier ring. The carrier ring is sandwiched between the line flanges. A Carrier Ring type Byepass Rotameter (BPC series) is available for pipe size from 25 mm to 450 mm NB. It can be designed to suit various types & pressure classes of line flanges. BPC series rotameters are normally manufactured as a complete unit comprising of a carrier ring with byepass arrangement and indicating Glass/Metal tube rotameter. The carrier ring is designed in one/two piece unit.

2. Flange Tapping: (Ref FIG.B) The pressure taps are drilled on the orifice flange which is welded to the main line pipe. The taps are at a distance of 24.5 mm from the orifice plate. The Byepass rotameter with flange tappings (BPF series) are available from 50 mm to 900 mm NB pipe sizes. Normally weld neck flanges are used. The scope of supply includes an orifice plate, a pair of orifice flanges ,indicating rotameter & byepass arrangement (optional).
3. D & D/2 Tapping: (Ref FIG.C) In this type the pressure tappings are drilled on the main pipe itself. The upstream tapping is at a distance of D which is internal pipe diameter from the orifice plate. The downstream tap is at a distance of D/2 from the orifice plate. The D, D/2 type byepass rotameters are available for line size of 50 mm to 1000 mm NB. The scope of supply includes an orifice plate and an indicating rotameter. The mainline flanges & byepass arrangement is normally in customer's scope.

Material of Construction

Orifice plate : 316 SS/EBONITE 'C'
Carrier rings : 316 SS/MILD STEEL/CS.
Orifice flanges* : ASTM-A-182/A-105
Orifice flanges std. : ASME B16.36
Pipe line : 316 SS/MILD STEEL/CS.
Wetted parts of the Rotameter : 316 SS/MILD STEEL/CS. OR Rubber Lined Steel**/PTFE Lined Steel**

** In case of D & D/2 Tappings

* In case of Flange Tappings only


Accuracy : +2% of Full Flow
Rangeability : 7 : 1 or 5 : 1
GTR Type : 10 : 1 on request
Rangeability MTR Type : 3 : 1
Accessories : High & Low flow alarms.
Transmitter : Against Specific Request.