1. Overview of Explosion Proof Submersible Pumps

An explosion proof submersible pump is a liquid-handling pump designed to

operate fully or partially submerged in fluid while complying with explosion protection

requirements for hazardous areas. These pumps are engineered so that any internal ignition

source is contained and cannot ignite the external explosive atmosphere.

1.1 Key Characteristics

• Motor and electrical components enclosed in an explosion proof housing.
• Designed to operate under liquid level, providing cooling to motor and seals.
• Suitable for hazardous areas classified as Zone 0, Zone 1, Zone 2, or Class I Division 1/2, depending on design.
• Typically used in flammable wastewater, hydrocarbons, industrial effluents, sumps, and pits in refineries, chemical plants, and fuel depots.

1.2 Typical Applications

• Refinery stormwater and oily water sumps
• Petrochemical plant drainage systems
• Fuel terminals and loading rack sumps
• Underground storage tank pits
• Hazardous wastewater treatment stages
• Mining and tunneling with explosive gas atmospheres

2. What Makes a Submersible Pump Explosion Proof?

The term explosion proof in the context of submersible pumps does not mean a

pump cannot explode; it means the design is capable of containing an internal explosion

without igniting the surrounding explosive atmosphere. This is often described with terms

such as Ex d (flameproof), Ex e (increased safety), or other protection

concepts depending on regional standards.

2.1 Common Explosion Protection Standards

2.2 Explosion Proof Construction Features

• Robust, flameproof motor enclosure with certified joints and flame paths.
• Sealed cable entries and glands with Ex certification.
• Surface temperature control to stay below specified temperature class (e.g., T3, T4).
• Specially designed mechanical seals and oil chambers to prevent ignition transfer.
• Use of anti-spark materials and non-sparking impeller designs where applicable.
• Integral thermal protectors, PTC sensors, and sometimes bearing temperature detection.

3. Common Issues With Explosion Proof Submersible Pumps

Although explosion proof submersible pumps are engineered for demanding environments, they

are still subject to mechanical, electrical, and process-related issues. Many typical

submersible pump problems are also present in explosion proof designs, but with added

safety implications because of the hazardous location.

3.1 Typical Problem Categories

4. Hydraulic and Performance Problems

4.1 No Flow or Very Low Flow

No flow from an explosion proof submersible pump is one of the most

frequently reported issues. It can be caused by simple system blockages or more serious

hydraulic mismatches.

4.2 Insufficient Flow or Reduced Capacity

Over time, an explosion proof submersible pump may suffer from reduced capacity

due to wear or process changes.

• Impeller wear from abrasive solids increases clearances and reduces efficiency.
• Partial blockage in the impeller, volute, or discharge piping restricts flow.
• Change in liquid properties (higher viscosity or presence of solids) affects performance.
• Voltage drop or under-voltage causes lower speed and reduced head.

In hazardous locations, variation in flow also impacts cooling of the explosion proof motor.

Continuous low-flow operation may lead to higher motor surface temperature and potential

non-compliance with the specified temperature class.

4.3 Cavitation and Air Entrainment

Cavitation occurs when local pressure drops below the vapor pressure of the

liquid, creating vapor bubbles that collapse inside the pump. In submersible pumps, inadequate

submergence, high fluid temperature, or excessive suction lift (in special cases) can promote

cavitation. Typical signs include:

• Crackling or rattling noise during operation
• Fluctuating discharge pressure and flow
• Gradual impeller erosion and pitting

Avoiding cavitation in explosion proof submersible pumps is important because:

• Severe cavitation can damage hydraulic components and upset pump balance.
• Mechanical shock and vibration shorten seal and bearing life.
• In extreme cases, vibration may affect explosion proof joints or cable integrity.

5. Mechanical Failures and Troubleshooting

5.1 Mechanical Seal Failures

Mechanical seals are among the most critical components in an explosion proof submersible

pump. They isolate the motor compartment from the pumped fluid and often operate in a

lubricated oil chamber.

5.2 Bearing Problems

Bearings support the rotating shaft and are essential to maintaining alignment between

impeller, motor rotor, and seals. Bearing issues can quickly lead to failure of the

explosion proof submersible pump.

• Overheating of bearings due to misalignment, overload, or inadequate cooling.
• Ingress of fluid through failed seals leading to lubrication loss or corrosion.
• Electrical discharge damage from variable frequency drives (VFDs) without appropriate mitigation.

Common troubleshooting steps:

• Measure vibration levels and compare with baseline values.
• Check motor current for signs of mechanical overload.
• Inspect lubricant condition during overhaul and look for contamination.
• Confirm that installation procedures follow the manufacturer’s Ex maintenance instructions.

5.3 Vibration and Noise

Excessive vibration in explosion proof submersible pumps is not only a mechanical concern but

also a safety issue because it can stress joints, fasteners, and cable glands.

6. Electrical Problems and Motor Protection

6.1 Motor Overheating

Motor overheating is one of the most serious issues in explosion proof

submersible pumps because excessive surface temperature can exceed the specified Ex

temperature class and compromise safety.

6.2 Nuisance Tripping and Protection Devices

Explosion proof submersible pumps often include multiple protective devices, such as:

• Thermal overload relays
• Embedded temperature sensors (PTC/RTD) in windings or bearings
• Moisture detection probes in the seal chamber or motor
• Ground fault protection devices

While these devices protect the pump and maintain Ex integrity, they can cause

nuisance tripping if not set or wired correctly:

• Verify set points according to the pump’s Ex-certified parameters.
• Check wiring diagrams to ensure correct sensor connections.
• Confirm control panel compatibility with the specific sensor types.
• Document all settings for future troubleshooting and audits.

6.3 Cable and Gland Problems

The submersible power cable and entry gland are critical to both electrical safety and

explosion protection.

• Inspect cable for cuts, swelling, or chemical attack from process fluid.
• Ensure that the gland is Ex-certified and correctly tightened to maintain ingress protection (IP rating) and flameproof integrity.
• Use correct strain relief to prevent tension on the gland and terminals.
• Check that cable size matches current rating and voltage drop requirements for the installed length.

7. Issues Specific to Explosion Proof Integrity

7.1 Damage to Flameproof Joints

Flameproof or explosion proof joints are machined interfaces between housing parts that

cool escaping gases from an internal explosion. Damage to these surfaces can invalidate

Ex certification.

• Avoid grinding, filing, or machining of Ex surfaces without manufacturer approval.
• Inspect for corrosion, pitting, or mechanical damage during overhauls.
• Use only approved gaskets and fasteners of the correct grade and length.
• Maintain required torque on bolts to ensure design gap and flame path dimensions.

7.2 Non-certified Parts and Modifications

Using non-certified spare parts on an explosion proof submersible pump can jeopardize

compliance and safety. Typical risky modifications include:

• Non-Ex rated cable glands or adapters
• Incorrect O-rings or seals with different compression characteristics
• Additional openings drilled into housings for sensors or drains
• Unapproved painting or coating that may obstruct flame paths or heat dissipation

In hazardous locations, any modification must be evaluated according to the original

certification documentation and applicable Ex standards.

7.3 Temperature Class Non-compliance

Each explosion proof submersible pump has a temperature class that defines

its maximum external surface temperature. Common classes include T1 to T6. Operating

conditions that increase temperature beyond the rated class are not acceptable in

explosive atmospheres.

• Monitor motor current and operating temperature via built-in sensors.
• Ensure continuous submergence within specified limits to support cooling.
• Avoid operation outside rated ambient and fluid temperature ranges.
• Review process changes (e.g., higher fluid temperature) and re-verify suitability.

8. Step-by-Step Troubleshooting Approach

Effective troubleshooting of explosion proof submersible pumps follows a structured

approach. The goal is to quickly identify root causes while maintaining safety in

hazardous areas.

8.1 General Troubleshooting Flow

1. Verify Safety Conditions

   • Confirm area classification and hot work requirements.
   • Follow lockout/tagout (LOTO) procedures and gas testing as required.

2. Gather Background Information

   • Review pump datasheet, curves, and Ex certificate information.
   • Collect operating history, alarm logs, and maintenance records.

3. Visual and Basic Checks

   • Inspect cable, gland, and external surfaces for visible damage.
   • Check for abnormal noise, vibration, or smell during operation.

4. Electrical Measurements

   • Measure line voltage, current, and phase balance.
   • Verify protection device settings and activation history.

5. Hydraulic Verification

   • Evaluate suction and discharge conditions, valve positions, and head.
   • Compare actual operating point with pump curve if data is available.

6. Removal and Detailed Inspection

   • Lift pump safely from sump according to manufacturer instructions.
   • Inspect impeller, seals, bearings, and enclosure joints.

8.2 Troubleshooting Matrix (Common Symptoms)

9. Preventive Maintenance for Explosion Proof Submersible Pumps

Proper preventive maintenance significantly reduces common issues and supports the explosion

proof integrity of submersible pumps. Maintenance must always be performed according to

Ex requirements and by competent personnel.

9.1 Routine Inspection Checklist

9.2 Storage and Idle Periods

Explosion proof submersible pumps may remain idle for extended periods in standby

applications. Idle conditions can lead to:

• Corrosion of stationary parts and seal faces
• Sticking of impeller or rotor
• Degradation of lubricants

Recommended practices:

• Periodically jog or run the pump for a few minutes under controlled conditions.
• Rotate the pump shaft manually (when not submerged and power isolated) according to instructions.
• Store spare pumps in a dry, temperature-controlled environment and protect machined interfaces.

10. Typical Specifications for Explosion Proof Submersible Pumps

Although specific explosion proof submersible pump specifications vary by model and

manufacturer, the following tables summarize common ranges and parameters that are

often referenced during selection, troubleshooting, and maintenance.

10.1 General Performance Range

10.2 Explosion Proof Ratings

10.3 Construction Materials

11. Selection and Installation Tips to Reduce Troubleshooting

Many common issues with explosion proof submersible pumps can be avoided through proper

selection and installation practices.

11.1 Correct Sizing and Application

• Match pump curve to system curve, ensuring operation near best efficiency point.
• Account for solids size, stringy materials, and abrasives when choosing impeller type.
• Verify explosion proof rating against area classification and gas group.
• Consider variable level conditions and potential for dry running.

11.2 Installation Best Practices

• Use guide rail systems to allow safe removal and accurate positioning.
• Design sumps with sufficient volume and submergence to prevent vortexing and air entrainment.
• Locate level sensors or floats to prevent rapid cycling and to keep the motor adequately submerged.
• Ensure correct cable routing and protection against mechanical damage and chemical exposure.

11.3 Control and Monitoring

• Integrate pump run status, alarms, and trip signals into plant control systems.
• Trend key parameters such as current, temperature, and number of starts.
• Use seal leakage detection and moisture sensors where available.
• Implement start/stop delays and alternation logic in dual pump systems.

12. Frequently Asked Questions About Explosion Proof Submersible Pump Issues

12.1 How do I know if my submersible pump is explosion proof?

An explosion proof submersible pump will have a clearly marked Ex nameplate, including

information such as protection type (e.g., Ex d, Ex e), gas group, temperature class, and

relevant certification markings (ATEX, IECEx, or local Ex scheme). The documentation

should include an Ex certificate and instructions specific to hazardous locations.

12.2 Can any electrician repair an explosion proof submersible pump?

Repairs and overhauls of explosion proof submersible pumps must be carried out by personnel

competent in Ex equipment maintenance, following applicable standards and the original

certificate conditions. Unauthorized repairs may void the explosion proof certification

and create safety risks.

12.3 What is the most common cause of failure in explosion proof submersible pumps?

Common causes include mechanical seal failures due to dry running, incorrect level control,

or abrasive fluids; electrical problems such as overheating or insulation breakdown; and

hydraulic issues like clogging or operating far from the best efficiency point. Many of these

are linked to installation or operating conditions rather than inherent design flaws.

12.4 How often should I perform maintenance on an explosion proof submersible pump?

The maintenance interval depends on operating conditions, duty cycle, and process fluid

characteristics. However, visual and operational checks should be performed at least

weekly, with detailed inspections and lifting of the pump typically done annually or

according to the manufacturer’s maintenance schedule.

12.5 Can variable frequency drives be used with explosion proof submersible pumps?

Variable frequency drives (VFDs) are commonly used with explosion proof submersible pumps,

but the motor and temperature protection must be suitable for inverter duty. Additional

measures such as bearing protection and correct parameter setting (minimum frequency, ramp

times, overload limits) are essential to avoid overheating and maintain Ex compliance.

13. Conclusion

Explosion proof submersible pumps play a vital role in safe fluid handling in hazardous

environments. Understanding common issues and troubleshooting techniques enables operators

to maintain reliability, minimize downtime, and preserve explosion protection integrity.

By focusing on correct selection, proper installation, regular preventive maintenance, and

disciplined troubleshooting procedures, most problems can be identified and resolved before

they lead to unsafe conditions or costly failures.

This reference guide provides a structured, SEO-friendly overview of common issues and

troubleshooting methods for explosion proof submersible pumps, highlighting hydraulic,

mechanical, electrical, and explosion protection aspects relevant to engineers, technicians,

and safety professionals working with Ex-rated submersible equipment.