The short answer is it depends. If you have a low flow rate meter then it may take longer than a higher flow rate meter. A good rule of thumb is to start with 5-10 minutes. Watch your flow readings to see if they seem higher than expected or if they are fluctuating. With low flows it may take 15-30 mins. Also, if you can vary the flow from low to high and back this will help to eliminate the bubbles. Proper orientation of the flow meter is also a factor, and in another blog, we discuss the influence of flow meter orientation. In most cases these methods will remove the bubbles.
What is the Best Orientation for My Flow Meter?
This is a critical question when it comes to flow meter performance. Ideally the meter would be mounted so that flow is along the horizontal position. In addition, if it is a paddlewheel type meter it is best if the paddlewheel is oriented vertically and not lying flat. Finally, if you have a low flow less than 2.5 GPM it is also helpful to have the flow ports at the top side of the meter. This will help in removing any trapped air in the meter. Air in the meter will cause the readings to read higher than actual.
If it is not possible to mount it in the horizontal position and it must be vertical it is in most cases important to have the flow going from bottom to top (upwards). This ensures that there is a full pipe to allow for accurate measurements. If not then you may have readings of no flow, lower than expected flow or erratic readings.
Should My Flow Meter be ROHS/REACH Compliant?
ROHS and REACH originated in the European Union in 2003 and 2007 respectively. ROHS (Restriction of Hazardous Substances directive) restricts the use
of 10 hazardous or potentially hazardous elements used in the manufacture of electronics and electrical equipment. There are a few exceptions.
REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) deals with the production and use of chemicals and the impact they may have on human health and the environment.
The EU requires compliance with ROHS/REACH requirements in order to sell Electronic/Electrical products and REACH listed chemicals in the EU countries. A large number of US states and companies now follow ROHS/REACH certification regulations.
In answer to the title question, from the standpoint of the environmental and health and safety considerations the answer is yes. If you purchase a product from an EU country or from a US company that exports their products, they most likely are compliant. You can generally find a ROHS/REACH statement on their company website and/or their product literature. If not a call to customer service should provide an answer.
How Long of an Inlet and Outlet Tube do I Need on My Flow Meter
This is a very common question in regard to installing a new flow meter. The answer depends on the type of flow sensor technology employed. In this article we will look only at paddlewheel type flow sensors. With this type of meter, the inlet is the most sensitive and critical to the performance of the flow meter. For example, if there were an elbow attached directly at the inlet there would be an excessive amount of turbulence induced into the rotor cavity. The accuracy of the flow reading will be affected. Measurements have shown that the accuracy may be affected by as much as 3%.
To maintain an accurate reading, it is recommended that a straight length equal to 10 pipe inner diameters be installed at the inlet of the flow meter. The outlet tube length does not have the same degree of consequence, but a straight run of at least 3 pipe inner diameters is recommended.
Another solution to this issue is to request the manufacturer to install the fittings and calibrate the meter with them in place. This nullifies the error factor.
In another article we will discuss the use of fittings and tubing and how they can affect accuracy.
Why Does Fluid Temperature Matter When Selecting a Flow Meter?
There are several reasons why fluid temperature matters when choosing a flow meter.
Temperature effects the fluid viscosity. Usually, the viscosity decreases as temperature increases and vice versa. This may affect the measurement accuracy of your flow meter unless viscosity offsets are employed. Please see application note, Why does fluid viscosity matter when selecting a flow meter for a detailed explanation.
When exceeding temperatures of +100o C or -40o C there are important safety factors to consider and it is suggested you speak to an applications engineer at the flow meter supplier about your specific application. Important considerations are: product safety, component temperature limits, and potential personal safety or operating environment considerations.
At temperatures at or approaching 0o C and at the ambient dew point, the buildup of ice on the flow meter is of concern. Your application engineer can suggest ways to reduce or eliminate icing concerns. At high temperatures the safety for personnel may be a consideration and protective shielding may be needed.
Proteus Industries has years of experience producing flow meters for extreme temperatures and in designing protective measures for flow meters operating at extreme temperatures.
Why Does Fluid Viscosity Matter When Selecting a Flow Meter
Flow meters are calibrated and/or specified at the viscosity of water at around 25 deg. C. This condition for water is considered a kinematic viscosity of 1 centistoke (cSt). In SI units this is 1 m^2/sec. Different flow meter types react differently to viscosity. Paddlewheel flow meters have pros and cons relative to some other types of meters.
In higher viscosity fluids, the paddlewheel calibrated for water will have a slower rotation as related to density. The result is that the reading will be lower than the actual rate of flow. Conversely, if the viscosity is less than 1 cSt, the paddlewheel will turn faster, indicating a higher than actual flow rate. Depending on the actual viscosity and the accuracy required for your application, this may or may not be an issue. If so, it is recommended that the flow meter be calibrated at the viscosity of the planned fluid. Functionally, paddlewheel flow meters can generally operate up to 100 cSt with a viscosity compensated calibration.
Vortex meters on the other hand are little affected up to 2 cSt. After that, there are curves and formulas that provide the compensated reading. The effect of viscosity is that the higher it goes, the lower the upper flow range of the Vortex meter becomes. For most purposes, after 5 cSt the vortex meter is not a good option.
If you are using a fluid other than water in your application, it is highly recommended that you discuss the application with an application engineer of the flow meter supplier.
Proteus Industries can perform custom calibrations to ensure your flow meter is matched to your fluids viscosity.
What is the Accuracy of My Flow Meter and How is it Determined?
The accuracy of the flow meter is defined as how close a reported value is to the true flow rate.
The accuracy is determined through the process of calibration. To accurately perform a calibration, a calibration stand is required. The stand would require a reference flow meter with an accuracy better than the expected accuracy of the meter under test. A typical accuracy of a reference meter is + or – .5%.
Also required are adjustable valves (either manual or automated), a method for collecting and recording the data (at several flow rates), and a way to calculate the accuracy. Depending on the sophistication of the flow meter, the unit being calibrated would be adjusted to the correct parameters to match the output signal to the flow.
In the case of a flow sensor with no adjustable electronics, or a Vortex meter with a factory fixed calibration, the unit can be characterized by measuring the flow and the meter output at several flow rates, collecting the data with the reference meter, and plotting the curve showing the difference between the two.
Accuracy is the degree to which the result of the measurement of the flow meter conforms to the reference meter. Most Proteus flow meters are in the range of +/- 2%-to-3% full scale.
Should My Flowmeter be RoHS/REACH Compliant?
The RoHS (Restriction of Hazardous Substances Directive) and REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) standards originated in Europe to specify and identify chemicals and other materials used in manufacturing that are environmentally harmful.
These are required certifications for any company shipping products to the EU and Great Britain and, the standards have been adopted by many industrialized countries and states.
Most of US companies, and those of other countries, now go through the certification process to comply with these standards. If you are an OEM purchasing a flow meter to be assembled into your product, it is likely to be required that all parts going into your product need to comply.
When purchasing a flowmeter, verify that the product you are planning to purchase complies. If this is not clearly stated in the product datasheet, then ask the flow meter manufacturer.
Proteus Industries complies with RoHS and REACH requirements.
How Do I Know What Flow Range to Select Before Purchasing a Flow Switch or Flow Meter?
When selecting a flow switch or flow meter, there are several things to consider. The rated flow rate of your pump is a good place to start, but keep in mind that the flow at the point of installation may not be the same as at the pump.
To find out the flow rate at the installation point, make a break in the line and use a bucket and a stopwatch to measure the amount of flow for one minute. You now have a good idea of the flow rate.
Ideally, you want to select the flow range of the meter so that your nominal flow is near the middle of the range. This will provide the most accurate and reliable measurement.
It is always a good idea to review your selection with a technical representative of the manufacturer.
At Proteus Industries, we offer a wide range of flow meter selection, which could be ideal for your application, and the technical support to help guide your selection.
How to Read a Rotameter : Points to Ponder
An instrument, which measures the volumetric flow rate of the fluid running through a closed conduit, is called a rotameter. The device consists of a float and a tube. Being a kind of a variable-area meter, it analyzes the flow rate by the upward and downward motion of the float in the tapered tube and the measurement provided by the flow meter is directly proportional to the area of flow and the flow rate.
Principle Involved in the Operation of the Rotameter
Now the question is how to read a rotameter? Rotameter is the most accepted industrial flow meter, which works based on the principle of gravity and variable area. The flow rate increases and decreases the height of the float, which accordingly adjusts the passage of the fluid flow and consequently, the total area between the float and the wall of the tube. Equilibrium is reached when the upward force created by the flowing fluid balances the descending force exerted by the mass of the float, hence maintaining a stable position of the float. The unit of the measurement is in liters or gallons per minute.
How to read a Rotameter:
Along with the float and tube, a rotameter may come equipped with an adjustment knob, which enables the user to set the flow rate according to their requirement. Let’s summarize the procedure for reading a rotameter:
- Connecting the rotameter with the fluid flowing source, to initiate the process.
- The float starts to swim in the middle of the tapered pipe due to the velocity of the fluid.
- The side of the meter has a scale. The lower and upper level of the float is to be measured by that scale, which gives the flow rate.
So, this is all about how to read a rotameter, which works in the combined effects of the velocity of the fluid, the gravity of the float, and annular area of the meter.
