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
What is the Accuracy of My Flow Meter and How is it Determined?
Should My Flowmeter be RoHS/REACH Compliant?
How Do I Know What Flow Range to Select Before Purchasing a Flow Switch or Flow Meter?
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.