Enquire US
Track order
Agent Login

Rotameter- Working Principle, Uses, Pros, Cons, and Handling


A rotameter variety known as a rotameter is also referred to as a variable area flowmeter. In commercial settings, it is used to gauge the velocity of air and liquids (such as water, oil, and others). In addition, it is utilised in medical devices like anaesthesia machines, oxygen tanks, and concentrators. The height and shape of these machines can vary between models, even for the same flow rate. The rotameter’s operating system will be discussed in this section.

In addition, we will discuss the rotameter’s pros, cons, and handling process of the rotameter.


Rotameter Working Principle

An outer vertically tapered glass tube with a wide top and a narrow base makes up a rotameter. It is referred to as a varying area flowmeter because the cross-sectional area of the tube varies. The tube has a measuring float inside. The glass tube has measurements embedded inside of it.


The float rests at the bottom of the tube when there is no fluid movement through the rotameter. The fluid forces the float upward as it enters the tube through the base. The pressure that the fluid applies to the float directly relates to the distance that the float travels from the foundation.


Advantages of Rotameter

A variety of benefits may be associated with the varying area flowmeter. The following list of rotameter’s benefits is provided.


  • It is inexpensive and widely accessible in the market.
  • It offers a linear measurement gauge. As a result,getting a reading is made easier.
  • Rotameter can detect fluids moving at velocities between 1 LPM and 10 LPM. In other words, it is appropriate for measuring fluids moving at low to middle speeds.
  • The rotameter can detect even corrosive fluids. This is due to the metal and glass cover being extremely resistant to different types of chemicals.
  • It offers greater sharpness and accuracy.


Disadvantages of Rotameter

  • The rotameter has some limitations despite being helpful in a variety of situations. Therefore, a few of the drawbacks are listed below.
  • Due to fluid pressure, the outer glass layer is readily breakable. Additionally, while the machine is being transported or maintained, the glass covering may crack.
  • Rotameter ought to be maintained erect. It will result in measurement errors if you angle it.
  • The fluid you’re going to use to gauge velocity needs to be transparent. You won’t be able to see the metering float correctly if you don’t. You won’t be able to take the measurement in that situation.
  • It is not appropriate for fluids moving at a fast speed.
  • There may be a case of parallax error if you do not place your eyes at the same level as the metering float.


Handling process

When using the rotameter, you must be mindful of the following.


  • The rotameter is made of a glass tube, so if you don’t handle it carefully, it could shatter.
  • The flowmeter should not be adjusted to “0” while it is in use. The pressurised air movement will be impeded by this. As a result, it may harm the rotameter permanently. A minimum flow rate of 0.5 gallons per minute is required.
  • While getting the reading, parallax errors must be avoided.
  • The glass’s exterior can be cleaned with an alcohol brush.
  • At the bottom of the flowmeter, the float can occasionally become trapped. The airflow will be obstructed by this. As a result, you won’t get any results from it. In this situation, flip the flowmeter over and attempt to shift the float away from the base. Try using a gust of wind to clear the obstruction if you are unable to invert the flowmeter.


What is Rotameter?


A flow-measuring instrument that measures the volumetric flow of versatile fluid with ±1.5% of full flow accuracy is called glass tube rotameter.


Rotameter Manufacturer:

Fidicon is one of the pioneering manufacturers in GLASS TUBE ROTAMETER, LOW FLOW ROTAMETER & ACRYLIC BODY ROTAMETER technology, Fidicon Devices India has created a contrasting and proven portfolio of flow measuring equipment’s, installed and in use across virtually every industry.


Rotameter: The meter’s operation is based on the variable area principle: fluid flow raises a float in a tapered tube, increasing the area for passage of the fluid. The greater the flow, the higher the float is raised. 


The height of the float is directly proportional to the flowrate. With liquids, the float is raised by a combination of the buoyancy of the liquid and the velocity head of the fluid. With gases, buoyancy is negligible, and the float responds to the velocity head alone. 


The float moves up or down in the tube in proportion to the fluid flowrate and the annular area between the float and the tube wall. The float reaches a stable position in the tube when the upward force exerted by the flowing fluid equals the downward gravitational force exerted by the weight of the float. 


A change in flowrate upsets this balance of forces. The float then moves up or down, changing the annular area until it again reaches a position where the forces are in equilibrium. To satisfy the force equation, the variable area flow meter float assumes a distinct position for every constant flowrate. 


However, it is important to note that because the float position is gravity-dependent, variable area meters must be vertically oriented and mounted.




  • With additional Jacketing.
  • Minimum Pressure Loss.
  • Accurate measurement even at higher flow.
  • Suitable for low flow.
  • Heavy Duty Design with maximum visibility.
  • Suitable for line installation.




  • Material of Construction of Wetted parts
  • Density of Fluid
  • Specific Gravity of Fluid at Operating Conditions               
  • Viscosity of Fluid at Operating Conditions
  • Operating Pressure & Operating Temperature
  • Measuring Range
  • Type of Connection
  • Flange Size/Rating




  • Accuracy: ±1.5% of full flow
  • Repeatability: 0.5%
  • Rangeability: 10:100                                                                     
  • Scale Length: 200mm, 250mm (Optional)
  • Flange to flange: 500 mm
  • Max. Temp.: Up to 200 0C
  • Max. Pressure: 10 – 15 kg/cm2
  • End Connection: Flanged or Threaded
  • Enclosure: IP 55 or IP65 on request




  • Material of Construction
  • Tube: Borosilicate Toughened Glass tube
  • Float & RETAINNER: SS316,                                                

PTFE, other on requirements

  • Packing: Neoprene, PTFE, Silicon
  • End Fitting: Mild Steel, SS304, SS316, Aluminium, PTFE Lined,

PP & PVC and any other desired material subject to its availability.

  • Frame & Cover: MS & SS Etc.
  • Scale: – Aluminium Acrylic, & SS
  • Gland :- CS, SS & GI Etc.





Rotameter  Installation : 

a)-Ensure to check all the documents including the calibration report dispatch checklist.

b)-If anything missing such as calibration/testing report and inclusive accessories etc.

Kindly coordinate with our sales team regarding same.

c)-Unpack the product with good handling practice. 

  1. d) -Carefully inspect the Rotameter for damage that may have occurred during transportation.

e)-Remove the inserted PVC rope into the tapered tube.

f)-Before installing the instrument assure to confirm your temp, pressure, fluid, and flow orientation as well as other requirement are suited with a rotameter.


To enhance the proper installation following prevention to be taken location selection criteria :


1-Avoid -misalignment of pipe.

2-Install the instruments vertically with bottom inlet / Top outlet port.

3-Maintain constant pressure-because instantaneous pressurization could lead tube damage/failure.

4-Recommended to install control valve on the both side bottom–inlet/Top-out let.

Bottom valve to be control once while top valve could be control multiple times as per requirement.

5-Huge change in fluid viscosity may lead flow error. Hence try to maintain contact viscosity.

6-Using of appropriate amount of sealant (Teflon tape) on external threads may prevent possible leakage.

7-Make sure to use suitable gasket on the inlet/out let connection end to maintain minor leakage and hassle free operation.

8-Keeping instrument till long in storehouse may leads minor rust strains.

Hence to avoid possible strain-rotameter should be cleaned with a relevant soap solution.

9-Handle with care during installation with good tooling practice.


Safety & precaution while installation:

1-While operating the instrument do not open in-let/Bottom valve suddenly it may lead broken of tube and other possible accidents.

2-During installation make sure the operation is shut down of the particular location where the instrument to be installed. 

3-Do not dis-assemble or modify the instrument yourself as it may not be return to its original form. And explosion-protected construction of the instrument might be disturbed. Which may cause serious hazards.

4-Use proper safety PPEs such as Hand gloves, Goggles, Helmet & Face-Shield / face mask etc. While installing /Uninstalling the instrument.

Rotameter Service / Maintenance :

1-During service/maintenance make sure the operation is shut down of a particular location where the instrument is already being installed.

2-Un-install the instrument carefully and avoid the touching of process fluid as it may be harmful.

3-Inspect the occurred issue on the instrument and meanwhile coordinate with our service engineer/check the identified part carefully and try to replace it with new – genuine Fidicon make part only.

4-In case of slurry and dusty fluid service may require in short duration.

In this case the measuring tube to be cleaned properly with the help of a suitable brush and soap water.

5-Dis-assemble the parts as per the below-given arrangement.

6-If occurred issue couldn’t be identified and the product falls under warranty – guarantee period.Please use our free onsite/in-house service.


Recommended spare for Glass Tube Rotameter: 1-Using Fidicon genuine spare may result in high accuracy/durability of the instruments.


Spares Model No. FDI-GTR-202 :

1-Tapered tube.


3-Packing set


5-Front cover

6-Side cover


8-Guide rod



2-Using fidicon make spare ensure hassle free operation.


Recommended disposal : 1-Give it back to us & we will take care of recycling & possible disposal.


2-User can dis-assemble the product into following categories:

1-Metals / alloys


3-PTFE/Polymer etc.

4-Any other.


The above may be handed over (State pollution board) , authorized re-cycler item-wise.