Troubleshooting Common Issues in High Flow Hydraulic Submersible Pumps

Understanding the Core of Submersible Pump Performance

High flow hydraulic submersible pumps are the workhorses of demanding dewatering, construction, and industrial applications. In environments where electric power is unavailable or hazardous, these pumps offer unparalleled reliability and power. However, their reliance on a complex interplay between the pump unit and the external hydraulic power unit (HPU) makes systematic troubleshooting an essential skill for operators and maintenance teams. Effective troubleshooting not only minimizes costly downtime but also extends the lifespan of the equipment. Common issues such as reduced flow rate, overheating, excessive noise, and failure to start can often be traced to a few key areas. This guide delves into these problems, providing a structured, expert approach to diagnosis and resolution, with a focus on maintaining the integrity of your hydraulic system and ensuring peak operational efficiency.

Problem 1: Reduced Flow Rate

A decline in the pump's output is often the first sign of trouble. This symptom can stem from a variety of sources, ranging from simple blockages to internal mechanical failures.

Possible Causes

• Blocked Intake (Strainer or Suction Line): The most common cause. Debris such as sand, silt, and fibrous materials can clog the intake screen or the suction hose, starving the pump of fluid. In Hong Kong's marine and construction environments, where sediment is prevalent, this is a frequent issue.
• Damaged or Worn Impeller: The impeller is the rotating component that imparts energy to the fluid. Over time, cavitation, abrasive particles, or corrosive chemicals can erode, chip, or crack the impeller blades, severely reducing pumping efficiency.
• Hydraulic Fluid Issues (Low Level, Wrong Viscosity, or Air Entrainment): The hydraulic system driving the pump motor is sensitive to fluid condition. Low fluid level in the HPU reservoir reduces pump efficiency. Fluid with incorrect viscosity creates internal leakage. Air in the fluid (aeration) causes spongy operation and power loss.
• Hydraulic Power Unit (HPU) Performance Problems: The HPU is the heart of the system. A failing pump within the HPU, a worn pressure relief valve (PRV) that opens prematurely, or an engine running below its rated RPM will all result in insufficient hydraulic flow and pressure reaching the submersible pump motor.

Troubleshooting Steps

1. Inspecting the Intake: Begin at the source. Shut down the system and safely secure it. Disconnect the suction hose from the pump. Visually inspect the hose for collapse or kinks. Examine the intake strainer or filter for blockages. Clean or replace as necessary. In many Hong Kong harbor dredging projects, a pre-filter is recommended to handle high solids loads.
2. Checking the Impeller: Access the pump's volute casing. Carefully inspect the impeller for signs of wear, pitting, or damage. Use a feeler gauge to check the clearance between the impeller and the wear plate. Worn clearances recirculate water internally, reducing output. Replacement of a worn impeller or wear plate is a standard repair procedure for hydraulic submersible pumps that have seen heavy use.
3. Evaluating Hydraulic Fluid Level and Condition: Check the sight glass or dipstick on the HPU reservoir. The fluid should be at the correct level. Sample the fluid. It should appear clear and smell fresh, not burnt. Conduct a simple blotter test on a paper towel to check for water contamination. Hydraulic fluid in Hong Kong's humid climate is prone to water ingress via condensation. If the fluid is milky or contaminated, it must be changed.
4. Assessing the HPU Performance: With the system running and the submersible pump connected, use a pressure gauge in the HPU's main pressure line to measure the system pressure. Compare this to the pump's required pressure specification. If the pressure is low, check the PRV setting. If the PRV is set correctly, the issue may be with the HPU's own pump. Listen for unusual noises from the HPU's pump, which could indicate wear or cavitation. Ensure the HPU engine throttle is set to the correct operating RPM for the required flow.

Problem 2: Pump Overheating

Overheating is a critical condition that rapidly degrades seals, bearings, and hydraulic motors, leading to catastrophic failure. It is a symptom of excessive thermal energy being generated and not dissipated.

Possible Causes

• Insufficient Cooling: Hydraulic submersible pumps rely on the surrounding water for cooling. If the water level is too low, the pump is operating in a very shallow puddle, or the water temperature is excessively high (e.g., >40°C), the pump cannot shed heat. Also, debris wrapped around the pump casing can insulate it.
• Overload: The pump is operating outside its designed performance curve. This can happen if the discharge head is too low (running the pump off the end of its curve, causing excess flow and high amp draw on the hydraulic motor) or too high (causing the pump to operate near shut-off head, generating heat with minimal flow). Operating the pump against a closed or partially closed discharge valve can also cause rapid overheating.
• Improper Hydraulic Fluid: Using fluid with the wrong viscosity grade for the ambient temperature creates excessive internal friction. Old, degraded fluid loses its lubricity and thermal conductivity, making the hydraulic motor run hotter.

Troubleshooting Steps

1. Ensuring Adequate Cooling: First, verify the pump is fully submerged. The minimum submersion depth is usually indicated in the manual, but a good rule of thumb is at least 12-18 inches of water above the pump's discharge port. Use a temperature gun to check the water temperature. Clear any debris from the pump's cooling fins or outer casing. For deep well applications, ensure the pump is sized appropriately for the well's drawdown to prevent exposure.
2. Verifying Load Conditions: Check the discharge valve position. Ensure it is fully open. Measure the pump's flow rate using a flow meter and compare it to the pump's performance curve at the measured discharge head. A flow significantly higher than the best efficiency point (BEP) is a sign of an overload condition. If possible, adjust the system head by throttling a valve (though this is not energy efficient) or check for an improperly sized impeller. Remember that an application like using a ZONDAR ZDHB20 Hydraulic Breaker requires a specific flow and pressure from the HPU; connecting a large pump that exceeds the HPU's oil cooler capacity will lead to system-wide overheating.
3. Checking the Hydraulic Fluid Type and Quality: Consult the pump and HPU manual for the correct fluid viscosity grade. In Hong Kong's tropical climate, a higher viscosity index fluid (e.g., ISO VG 46 or 68) is often recommended. Take a sample of the hydraulic fluid and send it for analysis. Key indicators of overheating are a high viscosity, low flash point, and the presence of oxidation byproducts. If the fluid is dark or smells burnt, change it immediately.

Problem 3: Excessive Noise or Vibration

Unusual sounds or vibrations are early warning indicators of mechanical distress. Ignoring them will lead to accelerated wear and eventual failure of components.

Possible Causes

• Cavitation: This occurs when the pressure at the pump inlet drops below the vapor pressure of the liquid, causing vapor bubbles to form and implode violently against the impeller and volute. It sounds like gravel or marbles rattling inside the pump. This is a classic symptom of a blocked intake or a very long, undersized suction line.
• Loose Components: Bolts holding the pump casing, motor mount, or discharge flanges can loosen over time due to vibration. A loose pump within its lifting cage will also cause a distinct clattering sound.
• Bearing Failure: The bearings in the hydraulic motor are critically stressed. Contaminated or degraded hydraulic fluid, along with normal wear, leads to bearing failure. The sound is often a low, rhythmic rumble or a high-pitched squeal that increases with load.

Troubleshooting Steps

1. Identifying Cavitation Symptoms: Listen for the distinctive sound. Feel the pump casing; it may vibrate intensely. A disassembly and inspection of the impeller will often show small, pitted areas (cavitation damage). The primary corrective action is to address the root cause: clear the intake blockage, increase the size of the suction hose, or shorten the suction lift. An alternative is to throttle the discharge valve to reduce flow, which can decrease the likelihood of cavitation.
2. Inspecting for Loose Parts: With the pump shut down and isolated, perform a thorough visual and physical inspection. Use a wrench or socket to check all accessible bolts on the pump casing, volute, and mounting brackets. Check the condition of the lifting cable or ears. Tighten any loose fasteners to the manufacturer's torque specifications. Check for excessive play between the pump and its support structure.
3. Assessing Bearing Condition: A simple diagnostic test is to use a mechanic's stethoscope or a long screwdriver against the pump's motor housing while it is running. Place the tip on the housing and the handle to your ear. The sound from failing bearings is distinct. A more definitive method is to check the hydraulic fluid for metal particles. If a magnetic plug in the HPU reservoir shows metallic debris, it strongly suggests bearing or pump wear. If bearing failure is suspected, the motor assembly must be disassembled by a qualified technician and the bearings replaced. A key step is to replace all hydraulic filters after a bearing failure to remove any debris.

Problem 4: Pump Not Starting

A pump that refuses to start can be frustrating, but the diagnosis is often systematic and can be resolved without immediate disassembly of the pump itself.

Possible Causes

• Hydraulic System Issues: The most likely cause is a problem within the HPU or the hose connections. A hydraulic lock can occur if the pump's motor is filled with fluid that is under pressure and cannot turn. Additionally, a seized pump motor due to internal rust or a foreign object will prevent rotation. The main hydraulic supply or return valves being in the closed position is a simple oversight.
• Control System Malfunction: Modern hydraulic systems incorporate solenoid valves, pressure switches, and electronic controllers. A blown fuse, a tripped circuit breaker, a faulty pressure switch, or a disconnected wire in the control panel can prevent the HPU from sending flow to the pump, or the pump's control valve from opening.

Troubleshooting Steps

1. Checking Hydraulic System Pressure and Connections: Start at the HPU. Ensure the engine or electric motor is running and at the correct speed. Verify that the HPU's main pressure line and return line isolation valves are open. Connect a pressure gauge to the main pressure line at the HPU outlet. Note the pressure. If it jumps to maximum system pressure immediately, the pressure relief valve is opening, indicating a blockage in the line going to the pump. Disconnect the hoses at the pump. If there is no flow when the system is engaged, check the HPU's pump operation. If the system pressure is zero, check the fluid level and the condition of the pump's drive coupling inside the HPU. Inside the pump, a seized motor can be felt by trying to manually rotate the pump shaft (if accessible) or by feeling for excessive resistance in the hose fittings.
2. Verifying Control System Functionality: Inspect the control panel of the HPU. Look for any alarm lights. Check all fuses and circuit breakers. Use a multimeter to test for voltage at the solenoid coil of the directional control valve that sends flow to the submersible pump. If voltage is present but the valve does not click when energized, the solenoid coil may be burnt out. If no voltage is present, trace the wire back to the controller. Check that safety interlocks (e.g., low oil pressure switch, high water temperature switch) are not activated. For remote start systems, verify the integrity of the remote cable or radio transmitter.

Proactive Strategies for Long-Term Reliability

Preventative maintenance is significantly more cost-effective than breakdown repairs. A structured program can anticipate failures before they occur.

Regular Inspections and a Culture of Vigilance

Implement a daily pre-operational check. This should include a visual inspection of all hoses and fittings for leaks or kinks. Check the pump's intake strainer for debris. Verify the fluid level in the HPU reservoir. Listen for any unusual sounds during the initial start-up. On a weekly basis, a more thorough inspection is warranted. This includes checking all bolts and fasteners, inspecting the pump's impeller through the suction opening for visible damage, and cleaning the pump's exterior of mud and debris that can act as an insulator. In corrosive environments like those found in Hong Kong's coastal reclamation projects, a monthly check for galvanic corrosion on the pump's sacrificial anodes is crucial. A logbook should be kept for every piece of equipment, including the ZONDAR ZDHB20 Hydraulic Breaker and the submersible pump, to track inspections and repairs.

Lubrication, Seals, and Fluid Management

While the pump's hydraulic motor is lubricated by the hydraulic fluid, many pumps have an upper bearing housing or a seal cavity that requires grease lubrication. Follow the manufacturer's schedule for greasing these points, using a high-quality, waterproof marine grease. Over-greasing can be as damaging as under-greasing, so use the correct amount. The mechanical seal is a critical component. Its failure allows water to enter the hydraulic motor, causing catastrophic damage. Some seals have a leak-detection port. Check this port periodically for drips of oil, which is an early sign of seal failure. The hydraulic fluid itself is the lifeblood of the system. Maintain it at the correct level and viscosity. Implement a regular fluid sampling program (every 500 hours or annually). A standard oil analysis report will provide data on viscosity, moisture content, acid number, and particle count. The presence of high levels of silicon often indicates dust ingress, while high levels of iron or copper point to internal wear.

The Imperative of Hydraulic Fluid Analysis

A dedicated fluid analysis program is the single most effective tool for predictive maintenance. For a fleet of hydraulic submersible pumps and associated equipment like hydraulic power units, this is not an option but a necessity. A professional analysis laboratory will issue a report that can be interpreted as a health scorecard for your system. Key metrics to track include:

By meticulously following these diagnostic and preventative procedures, you can ensure that your high flow hydraulic submersible pumps operate reliably, even in the most challenging applications. A proactive approach to maintenance, combined with a deep understanding of the hydraulic system's symbiosis, is the key to maximizing uptime and minimizing repair costs.