How to Replace O-Rings on a Hammonds Suction Calibration Gauge

The Hammonds Suction Calibration Gauge is used to verify additive injector suction performance and assist with calibration accuracy. Over time, O-rings can become worn, swollen, cracked, or chemically degraded from additive exposure and may need to be replaced.

Safety Precautions

Before servicing the gauge assembly, shut down fuel transfer operations, relieve all system pressure, close additive supply valves, and drain residual additive from the gauge assembly.

Wear safety glasses, chemical-resistant gloves, and protective clothing. Some additives, including FSII, CI/LI, SDA, and Biobor JF, may be hazardous. Always follow the safety data sheet and site procedures for the additive being handled.

Typical Signs O-Rings Need Replacement

• Additive leakage around the gauge body.
• Air entering the suction side.
• Erratic calibration readings.
• Loss of pump prime.
• Cracked, flattened, or swollen O-rings.
• Bubbles visible in suction tubing or the sight flow indicator.

Tools Required

• Small adjustable wrench.
• Allen wrenches, if equipped.
• O-ring pick, preferably plastic.
• Clean lint-free cloths.
• Compatible lubricant.
• Replacement O-rings.
• Mild cleaning solvent compatible with the additive.

Recommended O-Ring Materials

Material compatibility depends on the additive type. Common materials include Viton, PTFE, Neoprene, and Buna-N, though Buna-N should be treated as application dependent.

Always verify material compatibility with FSII, CI/LI, SDA, Biobor JF, and any other additive used in the system before installing replacement seals.

Step 1: Isolate the Gauge

Close the additive suction valve, depressurize the system, disconnect gauge tubing if necessary, and drain any remaining additive from the gauge.

Step 2: Remove the Calibration Gauge

Depending on the configuration, unscrew the gauge body from the mounting block or carefully remove the tubing fittings. Mark tubing orientation if required, and avoid twisting tubing excessively during removal.

Step 3: Disassemble the Gauge Assembly

Remove the retaining cap or body sections and separate gauge components carefully. Locate all O-rings, including face seals, stem seals, tube fitting seals, and internal plunger seals if equipped.

Step 4: Remove Old O-Rings

Use a plastic or brass pick to remove the old O-rings. Do not scratch sealing grooves, gouge aluminum surfaces, or use screwdrivers aggressively.

Inspect removed O-rings for swelling, cracks, flattening, and chemical attack. These conditions can help diagnose compatibility or contamination issues.

Step 5: Clean Components

Clean O-ring grooves, threads, mating surfaces, and internal passages. Remove crystals, dirt, tape debris, and additive residue.

This step is especially important on FSII systems, where moisture contamination may form deposits that interfere with sealing or suction performance.

Step 6: Inspect Gauge Components

Inspect the gauge for cracked housings, corrosion, scratched sealing surfaces, damaged threads, clouded sight sections, and loose fittings. Replace damaged components before reassembly.

Step 7: Install New O-Rings

Lightly lubricate O-rings with a compatible lubricant, then install them carefully into the grooves. Make sure each O-ring is not twisted, fully seated, and not pinched. Do not overstretch smaller O-rings.

Step 8: Reassemble the Gauge

Reinstall body components and tighten them evenly. Do not overtighten plastic or polycarbonate sections, since overtightening can distort seals, crack housings, or create suction leaks.

Step 9: Reinstall the Gauge

Reconnect tubing, verify flow direction if applicable, and make sure all fittings are secure. Use proper thread sealant where required. If PTFE tape is used, apply it carefully and avoid excess tape entering the system.

Step 10: Leak Test

Slowly reopen the additive supply and check for external leaks, air bubbles, loss of prime, and vacuum instability. Any suction-side air leak can severely affect calibration accuracy.

Step 11: Verify Calibration Performance

After O-ring replacement, run the additive pump and observe gauge response. Verify stable suction, smooth operation, and proper calibration repeatability.

Common Causes of O-Ring Failure

• Chemical incompatibility.
• Moisture contamination.
• UV exposure.
• Age or hardening.
• Excessive tightening.
• Pressure spikes.
• Improper storage of additives.
• Contaminated additive.

Recommended Preventive Maintenance

Inspect O-rings every 6 to 12 months, anytime calibration becomes unstable, during annual injector service, and whenever leakage is observed. On high-use systems, proactive replacement can prevent downtime and false calibration results.

Important Note on Suction Leaks

Even a very small suction-side air leak can prevent priming, reduce additive output, cause erratic injection ratios, and create false calibration readings.

On Hammonds systems, many calibration and performance issues trace back to suction-side sealing problems rather than pump failure.