How to install oval gear flow meter?

How to choose a suitable installation site for oval gear flow meter?

The oval gear flowmeter must be installed at an appropriate location, with strict attention to the following critical requirements:

1) The surrounding temperature and humidity should comply with the oval gear flow meter manufacturer's regulations, with a general temperature of -10 (-15)~40 (50) °C and humidity of 10%~90% .

2) Direct sunlight in summer can cause temperatures to rise; Places close to radiant heat can also cause an increase in temperature. Sunshade or insulation measures should be taken in such places.

3) Non-weatherproof instruments (non-dustproof/waterproof models) must be installed away from corrosive atmospheres or humid environments. Condensation formed by diurnal temperature fluctuations, combined with corrosive gases, can damage critical components such as the integrator's reduction gears. When unavoidable installation in such conditions is necessary, maintain a slight positive pressure inside the enclosure through a clean air purge system.

4) The installation location must be free from excessive vibration and mechanical shock. Areas with rotating equipment or heavy machinery should be avoided unless proper vibration isolation measures are implemented.

5) There should be sufficient space for installation and daily maintenance.

About oval gear flow meter flow direction and process connection

The oval gear flow meter shall be installed with perfect leveling and vertical alignment. The rotor shaft shall maintain parallel to ground level, except for vertically-oriented rotor shaft designs; other models shall be installed horizontally as specified in the operation manual. Refer to Figure 1 for typical installation schematic.

For reverse flow direction applications, the flowmeter and filter positions shall be swapped from the illustrated configuration. Adequate clearance shall be provided for filter screen removal and cleaning. In vertical installations, the PDF shall be mounted on a bypass line to prevent debris ingress from upstream piping.

The oval gear flowmeter shall be isolated from pipeline stresses including thermal expansion/contraction, deformation, and vibration. Improper valve/piping design-induced vibration shall be prevented, with particular attention to avoiding resonance conditions. Installation shall avoid mechanical stress caused by non-parallel flange faces, excessive flange gap distance, pipe misalignment and other improper piping configurations.

For oval gear flow meter with integrated pressure housings and measuring chambers, excessive installation stress may cause housing deformation, affect measurement accuracy degradation and even jam movable measuring components.

Preventing out of phase fluids from entering the oval gear flow meter

Oval gear flow meter feature minimal clearances between the measuring chamber and moving components. Particulate contamination in the fluid may cause component seizure and premature wear. A strainer shall be installed upstream with routine cleaning maintenance. For gas measurement, install protective devices when required, such as sediment traps or moisture absorbers.For liquid flow measurement applications, gas ingress into the piping system must be prevented. When necessary, a gas-liquid separator shall be installed upstream of the measurement device.

Mitigation Measures for Pulsating, Surge, and Overload Flows

While there are successful cases of installation on pump suction lines, the oval gear flow meters shall be installed on the pump discharge side as standard practice. Pulsating and surge flows can damage oval gear flow sensors. Ideal flow sources include centrifugal pumps and elevated head tanks.For applications involving reciprocating pumps or piping systems susceptible to overpressure surges (including water hammer effects), protective devices such as pulsation dampeners, expansion chambers and pressure relief valves shall be installed.

Overspeed operation of a elliptical gear flowmeter may cause irreversible damage. In systems where overload flow conditions may occur. Protective devices such as restriction orifice, constant flow valve and flow controller shall be installed downstream.

Non-interruption Installation

Due to the disadvantage of pipeline interruption caused by damage to elliptical gear flowmeter measuring components, a parallel system redundancy with automatic switching equipment should be equipped in places where continuous production or no interruption is allowed; The commonly used parallel operation mode with high flow can also be adopted, where one machine fails and the other can still flow.

Field Calibration

If on-site calibration of an oval gear flow meter using mobile standard volume pipes, standard meters, or other flow standard devices is required, branch pipes, connecting fittings, and shut-off valves should be pre-installed at appropriate locations on-site.

What are precautions for use of oval gear flow meters?

1) Pipeline Cleaning

Newly installed pipelines must be cleaned before operation, and subsequent flushing with actual fluid is often required to remove residual welding slag, scale, and other debris.This process should close the shut-off valves at both the inlet and outlet of the flowmeter to divert fluid through the bypass line.

If no bypass line is available, replace the flowmeter with a short pipe section temporarily.

2) Gas Purging

After initial fluid flushing, significant air pockets often remain in the pipeline. When pressurized operation begins, this trapped air can flow through the oval gear flow meters at excessive velocities, causing overspeeding of moving measurement components and potential damage to shafts and bearings. Therefore, at the beginning, the flow rate should be slowly increased to allow the air to gradually escape.

3) Bypass Pipe Switching Sequence

When switching the fluid flow from the bypass pipe to the instrument, the opening and closing sequence must be correct, and operations should be performed slowly—especially on high-temperature and high-pressure pipelines. As shown in Figure 2, the steps for activation are as follows:

• Step 1: Gradually open Valve A, allowing the liquid to flow through the bypass pipe for a period of time.
• Step 2: Gradually open Valve B.
• Step 3: Gradually open Valve C.
• Step 4: Gradually close Valve A.

For deactivation, follow the reverse sequence and actions.

After startup, use the lowest-position pointer or numeral wheel along with a stopwatch to confirm that excessive flow is not occurring. The optimal flow rate should be maintained at (70–80)% of the maximum flow rate to ensure the instrument's service life.

Figure 2 Bypass Pipe Switching Sequence

4) Filter Monitoring

The filter screen is most susceptible to damage during the initial startup of a new pipeline. After trial operation, promptly inspect whether the screen remains intact. Additionally, when the filter screen is clean and free of contaminants, record the pressure drop at normal flow rates. This parameter eliminates the need for future disassembly to check for clogging—instead, the extent of pressure drop increase can be used to determine whether cleaning is required.

5) Measuring High-Viscosity Liquids

For high-viscosity liquids flow measurement , heating is typically required to ensure flowability. When the elliptical gear flowmeter is shut down, the internal liquid cools and thickens. Before restarting, it must be reheated to reduce viscosity before allowing flow through the instrument. Otherwise, the thickened liquid may jam the moving measurement components, leading to instrument damage.

6) Lubrication

For gas-operated positive displacement flow meter, lubrication must be performed prior to startup. During routine operation, regularly check the oil level gauge to monitor lubricant volume.

7) Avoid Sudden Flow Rate Changes

When using a gas roots flow meter, it is important to avoid sudden flow rate changes (e.g., caused by quick-opening valves). Due to the inertia of the rotors, abrupt flow variations can generate significant additional inertial forces, potentially damaging the rotors.
If the flow meter is used as a detection flow instrument in a control system, a sudden closure of the downstream control valve may cause the rotors to continue rotating briefly, creating a compressor effect. This leads to a pressure increase downstream, followed by backflow, which can result in erroneous signals.

8) Steam used for pipeline flushing is prohibited from passing through the oval gear flow meters.

Troubleshooting for oval gear flow meters

1. Rotor Jamming in the metering Chamber

 Causes:
(1) Foreign debris entering the metering chamber from the pipeline;
(2) Solidification of the measured fluid;
(3) Water hammer or overload due to abnormal system operation, damaging the pins connecting the rotor and drive gear;
(4) Excessive wear of the drive gear bearings after prolonged use, causing rotor collision and jamming.

 Troubleshooting Measures:
(1) Disassemble and clean flowmeter; flush filters and pipelines.
(2) Implement thawing measures for solidified medium.
(3) Modify pipeline system to eliminate water hammer/overload; repair flowmeter.

(4) Replace bearings, drive gears or rotors; install new flowmeter if damage is irreparable.

2. Rotor Operates Normally but Counter Fails to Register

Causes:
(1) Damage to metering chamber seal output section, demagnetization of magnetic steel, or foreign matter jamming magnetic coupling;
(2) Loose gear disengagement in counter head;
(3) Malfunction of reset counter or totalizer counter;
(4) Loose pointer assembly.

Troubleshooting Measures:
(1) Disassemble and clean, or remagnetize components;
(2) Reinstall and adjust gear assembly;
(3) Remove and repair counter mechanism;
(4) Secure pointer fastening.

3.Flowmeter Measurement Inaccuracy

Causes:
(1) Significant temperature deviation with faulty automatic temperature compensator;
(2) Change in measured medium viscosity;
(3) Incorrect gear engagement in counter head after maintenance;
(4) Bypass valve not fully closed during operation, causing leakage;
(5) Actual flow exceeds specified range;
(6) Stiff movement of indicator mechanism or rotor contacting housing;
(7) Excessive flow pulsation;
(8) Gas entrainment in measured medium.

Troubleshooting Measures:
(1) Inspect and repair temperature compensation system;
(2) Recalibrate for current medium viscosity or select new meter suitable for medium;
(3) Remove counter head and properly reinstall gears;
(4) Ensure bypass valve is fully closed;
(5) Replace with properly sized flowmeter or adjust flow within specified range;
(6) Verify proper installation of rotor, bearings and drive gears; replace worn components;
(7) Implement pulsation damping measures;
(8) Install gas eliminator.

4.Excessive Flowmeter Noise

Causes:
(1) Broken rotor-drive gear pin causing rotor impact;
(2) Improper operation with excessive flow overload;
(3) Gas entrapment or system vibration;
(4) Bearing failure;
(5) Extended service beyond operational lifespan.

Troubleshooting measures:
(1) Remove and replace the rotor, scrape off any scratches or dents on the rotor;
(2) Install a flow limiting device downstream of the flowmeter;
(3) Inspect the system and eliminate vibrations;
(4) Replace the bearing, check if the filter is reliable, and reduce bearing wear;
(5) Replace the flow meter with a new one.

5.Flowmeter Leakage

Causes:
(1) Operating pressure exceeds the specified limit, causing housing deformation and leakage;
(2) Aging of rubber seals;
(3) Mechanical seal failure.

Troubleshooting measures:
(1) Verify system pressure gauge integrity, reduce pressure or replace the meter to maintain within rated limits; replace/repair severely deformed housings;
(2) Replace all degraded seals;
(3) Renew worn mechanical components or rubber parts.

6. Unstable Needle Movement (Sticking/Erratic Indication)

Cause:
Loose or stiff linkages in the indicator drive mechanism.

Troubleshooting measures:
Secure all connections and lubricate moving parts.