Introduction
1.1 What Is a Hydraulic Gear Pump?
A hydraulic gear pump is a type of positive-displacement pump widely used in hydraulic systems. It moves fluid by trapping a fixed volume in the gaps between rotating gears and then forcing the fluid out under pressure.
There are two primary types:
- External gear pumps: Two identical gears mesh externally, one driven by a motor (the driver), the other an idler.
- Internal gear pumps: A smaller internal gear meshes with a larger outer gear. Often includes a crescent or partition to help seal the suction side from the discharge side.
Key characteristics:
Fixed displacement: each revolution delivers a consistent volume of fluid.
Capable of handling high viscosity fluids and providing steady flows.
Relatively simple mechanical design with few moving parts, making them more maintainable and robust if properly used.
Why Gear Pumps Matter & Where They Are Used
Some common applications include:
Lubrication systems, where precise delivery of lubricant is required to protect bearings and moving parts.
Hydraulic power units in manufacturing, construction, and material-handling equipment such as presses, lifts, or mobile machinery.
Fluid transfer of viscous or abrasive fluids in chemical, petroleum, and food & beverage industries.
Because gear pumps are often integral to large systems, their performance (flow rate, pressure, temperature) has a direct impact on the efficiency, safety, and cost of operations.
Symptom 1: Unusual Noise
What Does "Unusual Noise" Mean?
When a hydraulic gear pump is operating normally, you expect a low hum or a gentle mechanical sound. Unusual noises are those that are new, louder, or different in quality: whining, knocking, rattling, hissing, or metallic grinding. These noises often indicate internal issues.
Causes of Unusual Noise
Several underlying issues can lead to unusual noise in a hydraulic gear pump. Here are the most common:
- Cavitation: When vapor bubbles form in the fluid (often because pressure drops too low at the pump inlet) and collapse in high-pressure regions. This generates a steady whining or screeching noise. Over time, it damages metal surfaces.
- Aeration: This occurs when air enters the pump, often through leaks, poor seals, or loose fittings, especially on the suction side. The noise from aeration tends to be more erratic, like rattling or gurgling. Air bubbles may also foaming in the reservoir.
- Excess fluid viscosity or cold oil: Thick or cold fluid flows more slowly, increasing internal friction and strain; this can intensify noise. Also, it can combine with cavitation if fluid doesn't reach the pump inlet fast enough.
- Obstructions or restrictions in suction line: Filters, strainers, hoses, or fittings that are clogged, undersized, or poorly installed can reduce inlet flow, lowering suction pressure and causing noise.
- Mechanical wear and misalignment: Worn gear teeth, damaged bearings, misaligned couplings, or loosened parts can cause metal-on-metal contact or vibration, generating knocking or grinding sounds.
Remedies & Preventive Tips
Once you've diagnosed what is likely causing the noise, here are ways to fix or prevent it:
- Ensure suction lines are clean, free of blockages, appropriately sized, and correctly installed ("no sharp bends, too many fittings, or restrictions").
- Inspect and maintain seals, especially shaft seals, and tighten or replace any loose or leaking fittings.
- Maintain fluid temperature and viscosity in the correct range. Warm up cold fluid before load; choose appropriate hydraulic oil grade.
- Avoid running the reservoir level too low; low fluid levels can draw in air or cause vortex formation.
- Use filters / strainers and ensure they are cleaned or replaced on schedule.
- Reduce pump speed if possible when under poor inlet conditions (cold fluid, high altitude, low reservoir volume).
- Monitor for early signs of damage (metal wear, rising vibration, worsening sound) and act promptly.
Symptom 2:Loss of Pressure or Reduced Flow
What Does "Loss of Pressure / Reduced Flow" Look Like?
When a gear pump begins to suffer from pressure loss or reduced flow, its symptoms may include:
- Actuators or cylinders moving more slowly than expected
- Machinery lifting less weight or lacking force
- Longer cycle times or sluggish response under load
- Failure to reach normal operating pressure
- Overall drop in system performance even though pump is running
These symptoms point to the pump not delivering the needed hydraulic power, often because it is not building or maintaining pressure appropriately or because flow is being lost somewhere.
Common Causes
Several underlying factors may lead to reduced pressure or flow in a hydraulic gear pump system:
- Internal leakage / volumetric inefficiency: Over time, wear in gear teeth, worn bearings, or enlarged clearances between stationary parts (e.g., end plates, housing) allow internal bypass of fluid, reducing actual output.
- Damaged or deteriorated seals: Seals that are worn, cracked or improperly installed let fluid escape before it contributes to pressure at the outlet.
- Obstructed suction / inlet path: A clogged strainer, undersized suction piping, a dirty filter, or poor reservoir design can limit the amount of fluid entering the pump, reducing flow and making it difficult to build pressure. This also contributes to cavitation or aeration.
- Fluid issues (viscosity, contamination, temperature): If the hydraulic fluid is too viscous (especially at low temperature), too thin, or contaminated with particles or air bubbles, it impacts pump efficiency and flow. Overly hot fluid can thin out and leak more easily; cold fluid may resist flow.
- Pump speed or drive problems: If the pump is not driven at the right speed (too slow, wrong rotation), or if motor coupling / drive alignment is off, the pump may not deliver rated flow or pressure.
- Relief or bypass valve issues: Relief valves set too low, stuck open, or bypass components leaking can reduce system pressure. Also, if downstream components are bypassing or leaking, that back-leakage reduces effective pressure.
Remedial Actions & Preventive Measures
Once you identify where the loss is coming from, these remedies help restore proper flow and pressure, and prevent recurrence:
Replace or repair worn seals, bearings, or other leakage-prone components.
Re-machine or replace parts with excessive internal clearance, such as gear mounting surfaces, end plates, or wear plates.
Clean or replace filters, strainers; ensure suction lines are free of restrictions, of correct diameter, and properly routed.
Ensure hydraulic fluid is appropriate viscosity, clean, and at proper temperature; change fluid if contaminated.
Check drive conditions: correct pump speed, proper coupling, correct rotation.
Adjust or service relief / bypass valves: ensure they are set correctly and functioning (not stuck open).
Maintain oil reservoir (supply) levels, proper breather caps, avoid air ingress.
Symptom 3: Overheating / High Temperature
What Counts as "Overheating"
Hydraulic gear pumps naturally generate heat during operation, but overheating happens when the temperature rises above what the pump and fluid are designed to tolerate. Typical warning signs include:
- Hydraulic fluid temperature exceeding ~180 °F (≈ 82 °C). Above this, many seal compounds degrade, and lubricant properties worsen.
- Pump body, hoses, or casing becoming hot to the touch even during moderate loads.
- Increased thermal expansion, which may cause leaks, seal failures, or loss of alignment.
- Darkening of hydraulic fluid, foul smell, or foaming in reservoir.
Common Causes of Overheating
Here are typical reasons why a hydraulic gear pump might overheat:
| Cause | How it leads to overheating |
|---|---|
| Contaminated fluid (dirt, water, particles) | Contaminants increase friction, clog filters, reduce cooling, and may cause fluid degradation. |
| Aeration and cavitation | Air bubbles (aeration) or vapor bubbles (cavitation) collapse, releasing heat; also reduce lubricant film and increase wear. |
| Low or inadequate fluid level (oil starvation) | Insufficient fluid cannot absorb heat or adequately lubricate; exposed components run hotter. |
| Wrong fluid type or viscosity | Fluid too thin loses lubrication, fluid too thick increases resistance and friction under load. Both cases cause extra heat. |
| Restricted cooling / blocked heat exchangers | If heat exchangers are dirty or damaged, airflow or coolant flow is blocked, so heat is trapped instead of dissipated. |
| Excessive load or system inefficiencies | Operating above design pressure or flow rates, leaks or poor component efficiency (valves, fittings) convert more energy into heat. |
Remedies & Preventive Measures
To reduce and prevent overheating, apply the following:
Use clean hydraulic fluid; filter or replace fluid regularly. Maintain strainer / filter elements so they do not clog.
Ensure fluid level is adequate; avoid running the pump near empty. Maintain proper reservoir design for cooling (size, airflow, ventilation).
Use correct fluid viscosity and grade: verify manufacturer's recommendations and consider ambient temperature / operating load.
Maintain cooling system components: clean or replace heat exchangers; ensure air flow, fans, or cooling water is sufficient.
Avoid overloading the pump: stay within rated pressure and flow; ensure relief valves and other control valves are correctly set and working.
Early detection of leaks, worn components, or internal inefficiencies; replace worn seals or bearings before they fail.
Diagnostic & Maintenance Checklist
Use this checklist regularly (daily, weekly, monthly as needed) to catch problems early and prolong the life of your gear pump.
| Frequency | What to Inspect / Test |
|---|---|
| Daily / Before Use | • Check fluid level in reservoir; top up if low. • Listen for unusual sounds (whining, knocking) and feel for abnormal vibration. • Check for visible leaks at fittings, hoses, seals. • Monitor operating temperature; ensure fluid & pump are not overheating. |
| Weekly | • Inspect filters / strainers: clean or replace if clogged. • Check hoses, pipelines, connections for wear, kinks, damage. • Inspect breather caps and fill screens; ensure reservoir breather is clean. • Observe fluid condition: look for discoloration, foam, smell. |
| Monthly / Periodic | • Analyze fluid sample for contamination (particles, water), viscosity, oxidation. • Inspect alignment of pump and driver (couplings, shafts) to prevent vibration and undue wear. • Inspect seals, bearings, and replace worn components. • Clean or service cooling equipment (heat exchangers, radiators, airflow vents). |
In summary, hydraulic gear pumps are powerful and reliable components in many industrial and mobile systems - but they are not immune to failure. Recognizing the three common symptoms early can save you time, money, and prevent serious damage:
- Unusual Noise - such as whining, knocking, or gurgling often signals issues like cavitation, aeration, or mechanical wear.
- Loss of Pressure or Reduced Flow - manifested in weak actuator force or slower-than-normal movement, often caused by internal leakage, clogged filters, or wrong fluid viscosity.
- Overheating / High Temperature - fluid or pump body running above design limits, which degrades seals and fluid, increases wear, and reduces efficiency.
Final Thought & Partner Suggestion
Proactive care and awareness are the best defenses against hydraulic gear pump failure. If you equip yourself (or your maintenance team) with the knowledge of what to listen for (noise), what to measure (flow/pressure), and what to watch (temperature/fluid condition), you'll significantly extend pump life and avoid costly downtime.
If you're looking for a reliable supplier or partner in hydraulic solutions, Poocca Hydraulic (Shenzhen) Co., Ltd. is worth considering. Founded in 2006, Poocca integrates research & development, manufacturing, maintenance, and sales of hydraulic pumps, motors, valves, and accessories. They offer a wide product range including gear pumps, with rigorous quality controls and certifications (such as ISO9001:2015).
