Accurately measuring fluid flow is critical in many industries. Rotary flow meters are widely used. However, the question remains: Can they be used to measure the flow of piston pumps? The answer is no. This article analyzes the reasons for this limitation.
Table of contents
- Introduction to piston pumps
- Introduction to the rotary flowmeter and its operating principle
- Flow characteristics of piston pumps
- Reasons why piston pumps cannot use rotary flow meters
- Alternative methods for measuring piston pump flow
- Finally
1. Introduction to the piston pump
A piston pump is a positive-displacement pump that pumps fluids through the linear motion of a piston or plunger within a cylinder. Such pumps are commonly used in industries such as oil and gas, petrochemicals, food, and pharmaceuticals.
Advantages of piston pumps:
- Generates very high pressure.
- Variable and pulsating flow
- High efficiency
- Can pump liquids of different viscosities.
2. Introduction to the rotary flowmeter and its operating principle.
A liquid flow meter is one of the simplest and most common devices for measuring liquid flow and works on the ejection principle.
The main components of a rotary flowmeter:
- a conical tube made of glass or metal
- A swimmer moving in a tube.
- measuring scale
Operating principle:
Fluid enters the flowmeter from below and moves the float upward. As the flow rate increases, the float rises, and its position on the scale indicates the flow rate.
3. Flow characteristics of piston pumps
The output flow of a piston pump has unique characteristics that make the use of a rotary flow meter challenging:
a) Pulsating character of the current:
- The movement of the piston or plunger creates an alternating current.
- In each cycle, the flow rate changes from zero to its maximum value and then back to zero.
- Rotation counters cannot detect these rapid fluctuations.
b) Rapid changes in flow rate:
- The flow rate is constantly changing.
- Flow meters are designed to deliver a constant flow rate.
- The ship is unable to adjust its position based on its current speed .
c) Hydraulic shock absorber:
- Sudden switching of the air flow on and off can cause severe electric shocks.
- These effects can damage the structure of the rotameter.
4. Reasons why piston pumps cannot use rotary flow meters
4.1 Limitations when working with rapid changes
Rotary flowmeters are used to measure constant flow rates. They respond slowly and cannot handle the rapid changes in flow rates that occur in piston pumps. The float of a rotary flowmeter cannot change its position quickly due to inertia and friction.
4.2 Large measurement error
Because the flow rate constantly fluctuates, the rotameter’s float fluctuates between minimum and maximum values, making it difficult to read the correct value. These fluctuations can lead to measurement errors of up to 50% or more.
4.3. Mechanical fragility
Flow pulsations and hydraulic shocks caused by the operation of a piston pump can lead to the following consequences:
- The glass tube of the glass rotary flowmeter is broken.
- Deformation of mechanical parts
- Rapid corrosion of floats and pipes.
4-4. Cavitation and bubbles
Pressure fluctuations in piston pump systems can lead to bubbling or cavitation , which can affect flowmeter performance.
4.5 Calibration problems
The rotary flowmeter is calibrated for a steady flow. Under pulsating flow conditions, the calibration conditions change , and the measurement accuracy decreases.
ACCUDRAW primary fluid systems
5. Alternative methods for measuring piston pump flow
5-1. Using the measuring container
- The easiest way to measure average consumption
- It collects liquid in a storage tank for a certain period of time.
- Measure the volume and calculate the average flow rate
5-2. Displacement flowmeter
- Suitable for pulse current
- High precision
- For example: piston, gear and diaphragm flow meters.
5-3. Electromagnetic flowmeter
- Insensitive to rapid current changes
- Conductive liquid required
- relatively high price
5-4. Ultrasonic flowmeter
- The transit time method is applied to the pulse current.
- Installation without contact with liquids
- Possibility to measure the instantaneous flow rate
5-5. Use of a pacemaker
- Install dampers on the pipes to reduce vibration.
- Once the vibrations have been reduced, a rotary flow meter can be used.
- Additional costs for the installation of shock absorbers
6. Conclusion
Due to the rapid vibrations and strong pulsations typical of piston pumps, rotary flowmeters are unsuitable for flow measurement in these pumps. Their main disadvantages are slow response time, large measurement errors, susceptibility to mechanical damage, and difficulty in calibration. In these cases, alternative methods such as positive displacement flowmeters, magnetic-inductive flowmeters, or ultrasonic flowmeters are preferable. The selection of a suitable measurement method should be based on criteria such as the required accuracy, cost, type of medium, and operating conditions.