Overview
This page provides detailed instructions for the installation, operation, maintenance, and troubleshooting of threaded and wafer-style flowmeters used to measure liquid and gas flow. The meters operate based on differential pressure measurement and display the flow rate mechanically or electronically. DOWNLOAD THE IOM MANUAL FROM OUR DIGITAL DOWNLOADS LINK IN THE MENU ABOVE UNDER DOWNLOADS!
1. Principle of Operation
- Flow rate is measured by the pressure differential across a machined flow nozzle in the meter body.
- Opposed bellows sense this pressure difference and move a mechanical linkage to drive the flow indicator needle.
- For digital versions, the bellows and linkage are replaced with a solid-state differential pressure sensorIOM.
2. Installation Planning
- Choose a location with easy visibility and service access.
- Ensure 10 pipe diameters of straight piping upstream of the flowmeter for accurate readings.
- Flowmeters are calibrated for Schedule 40 pipe; avoid tubing or hoses without proper transition.
- Avoid water hammer, vibration, or freezing conditions.
- Outdoor or splash-exposed meters should use a gasketed caseIOM.
3. Installation
3.1 Safety
- Never exceed pressure or temperature limits marked on the nameplate.
- Overpressure can cause injury or permanent meter damage.
- Contact the factory for high-temperature applications.
3.2 Dial Orientation
- The dial face can be rotated in 90° increments for better readability by removing four screws (do not remove housing screws)IOM.
3.3 Horizontal ↔ Vertical Conversion
- Rotate the dial and reinsert using locating indents.
- After reorientation, re-zero using the fine adjustment procedure.
3.4 Threaded Bodies
- Use proper thread sealant; ensure threads are clean and free of burrs.
3.5 Wafer Bodies
- Mount between flanges, ensuring gaskets are centered to prevent flow errorsIOM.
4. Operation and Maintenance
4.1 Preventive Care
- No routine lubrication required.
- Keep housing clean and dry; protect from corrosives and solvents.
4.2–4.5 Zero and Pointer Adjustments
- Zero check ensures the pointer aligns with the zero mark when no flow is present.
- Use coarse or fine adjustment to restore correct zero and pointer spring tension.
- The cam nut and stop nut regulate pointer movement and prevent bellows damageIOM.
4.6 Flow Calibration
- Factory calibrated; can be verified in the field.
- Meter should indicate within ±3% of full scale at 50% and 90% flow.
4.7 Cleaning
- Remove the housing and clean pressure ports and snubbers with gentle methods.
- Replace if clogged; reassemble with care to seal O-rings.
4.8 Reed Switch Adjustment
- Used for setting electronic trip points or alarms.
- Adjust switch position until it activates at the desired flow rateIOM.
5. Troubleshooting
| Problem | Likely Cause / Remedy |
|---|---|
| Pointer fluctuates | Turbulence; increase upstream distance or use heavy-duty snubbers. |
| Zero drift | Water hammer; modify piping or operation. |
| Slow response | Spring preload too low or pressure ports clogged. |
6. Correction Factors
6.1 Liquid Service
- Apply correction factor J when actual fluid specific gravity differs from calibration: Actual flow=J×meter reading\text{Actual flow} = J \times \text{meter reading}Actual flow=J×meter reading
6.2 Compressed Gas Service
- Apply correction factor K for different pressure or temperature: Actual flow=K×meter reading\text{Actual flow} = K \times \text{meter reading}Actual flow=K×meter reading where KKK depends on inlet pressure (Pa, Pc) and temperature (Ta, Tc)IOM.
7. Summary and Best Practices
- Ensure proper installation alignment, sealing, and orientation.
- Re-zero after adjustments or cleaning.
- Prevent mechanical stress, vibration, and overpressure.
- Periodic inspection of zero, reed switches, and cleanliness ensures long-term accuracy.
- Correction formulas allow use with various fluids and gases without factory recalibration.
PROBLEM: After installing the flow meter, the needle immediately pinned.
The problem was a sudden pressure surge (water hammer or startup shock) that created excessive differential pressure across the nozzle when flow began.
This drove the matched opposed bellows and mechanical linkage hard against the full-scale mechanical stop, pinning the pointer/needle at maximum. The manual repeatedly warns about exactly this risk:
- Section 2 (Installation Planning): “Avoid placing the flow meter where it will be subjected to water hammer and mount the flow meter rigidly to minimize shock or vibration.”
- Section 4.2 (Checking Zero): “Water hammer or pressure surges can displace the bellows and cause the zero to shift.”
- Section 5.2 (Troubleshooting – Zero Shift): Frequent re-zeroing indicates excessive water hammer.
- Section 4.4 (Coarse Zero Adjustment – IMPORTANT note): The stop nut must halt the center shaft before the bellows hit the cell cap. If they do hit, the bellows or cap can be damaged, causing leaking or permanent meter error.
Other contributing factors that can make this happen instantly on startup:
- Stop nut / cam nut out of adjustment (so the pointer can slam past or hard against the stop – see pointer preload check in 4.3).
- Flow started too abruptly (no gradual valve opening).
- Pulsation snubbers clogged or missing (they dampen surges; standard on gas meters and most liquid meters – see 4.7 and 5.1).
(It is not listed verbatim in the Troubleshooting section 5, but every symptom and warning points directly to surge/overtravel.)
You can usually be fixed in the field (unless the bellows were permanently damaged). Follow these steps exactly (with flow stopped and pressure relieved):
- Remove the lens (do not remove the pointer).
- Check zero (4.2). If the pointer is more than ½” (12 mm) off the zero reference point, go to Coarse Zero Adjustment (4.4):
- Set the stop nut so the pointer stops near the 6 o’clock position (factory mark is the “U” in “USA”).
- Adjust the cam nut until the pointer sits exactly on the zero reference mark.
- IMPORTANT: Manually move the center shaft and confirm the stop nut contacts the cell block before the bellows can hit the cell cap.
- Verify pointer preload (4.3): Rotate pointer CCW toward full scale – it must stop exactly at full scale (not beyond). Readjust cam nut if needed.
- If only a tiny tweak is required, you can use Fine Zero Adjustment (4.5) – but do not use it if you have reed switches or a 4-wire transmitter (use coarse only).
- Gently tap the housing to overcome friction, test that the pointer returns quickly and freely when rotated ~30° and released.
- Clean pressure ports/snubbers if debris is suspected (4.7).
- Reinstall lens, then verify calibration at ~90 % and 50 % of full scale (4.6). The meter must read within 3 % of actual flow.
Prevention for next time:
- Always start flow gradually (open valve slowly).
- Keep 10 pipe diameters of straight pipe upstream.
- Use heavy-duty (smaller-hole) snubbers if surges are common.
- Never exceed nameplate pressure/temperature limits (3.1).
If after adjustment the pointer stays pinned, doesn’t return smoothly, or you see leaking, the bellows or cell cap was damaged – return the meter to the factory for repair/recalibration (NIST-traceable service is available).
Follow the exact procedures in sections 4.2–4.5 and you will almost certainly get it working again.