A high-temperature circulation pump should be selected according to the actual liquid, normal and maximum temperature, viscosity, required flow, total head, system pressure, pump materials and sealing structure.

Motor power or connection size alone cannot determine whether a pump is suitable. The final selection should be based on the complete operating conditions and the pump performance curve.

What Is a High-Temperature Circulation Pump?

A high-temperature circulation pump continuously moves hot water, thermal oil or another heat-transfer liquid through an industrial heating or temperature-control system.

It may circulate liquid between a heater and production equipment, including:

• Mold temperature controllers
• Plastic injection molding machines
• Plastic extrusion equipment
• Rubber processing machinery
• Die-casting equipment
• Industrial boilers and heating units
• Heat exchangers
• Rollers, presses and laminating equipment
• Food and pharmaceutical processing equipment
• Chemical process systems

The pump must maintain sufficient circulation at the required temperature while operating safely within its hydraulic, mechanical and material limits.

1. Identify the Circulating Liquid

The first selection step is to identify the exact liquid being pumped. Different heat-transfer liquids have different temperature, viscosity, corrosion and lubrication characteristics.

Hot Water

Hot water offers effective heat transfer, but system pressure must be controlled to prevent boiling at the operating temperature. Water quality and treatment additives may also affect corrosion and material selection.

Thermal Oil

Thermal oil is commonly used when operating temperatures exceed the practical range of a water system. Its viscosity may be significantly higher during cold startup than during normal high-temperature operation.

Provide the oil name or specification, startup temperature, normal operating temperature and viscosity data whenever available.

Chemical Heat-Transfer Liquids

If the liquid contains chemicals, solvents or corrosive components, provide its complete name, concentration and relevant safety information. Pump materials must be checked for chemical compatibility.

Do not describe the liquid only as “oil,” “water” or “chemical” when more detailed information is available.

2. Confirm Normal and Maximum Temperature

The pump supplier needs both the continuous operating temperature and the maximum possible temperature.

For example, a system may normally operate at 150°C but briefly reach a higher temperature during startup, production changes or equipment malfunction. Selecting only according to the normal temperature may result in unsuitable materials or internal components.

Temperature may affect:

• Pump casing strength
• Internal bearing materials
• Mechanical seal materials
• Magnetic coupling performance
• Gaskets and elastomers
• Thermal expansion
• Motor heat protection
• Liquid viscosity and vapor pressure

The highest possible temperature should remain within the allowable range of the complete pump assembly, not only the pump casing.

3. Determine the Required Flow Rate

Flow rate is the amount of liquid that must circulate through the system within a specified time. It may be expressed in liters per minute, cubic meters per hour or gallons per minute.

Required flow depends on:

• System heating capacity
• Required temperature stability
• Supply and return temperature difference
• Heat-transfer liquid
• Equipment and mold design
• Number of circulation channels
• Pipe dimensions

A pump should not be selected only from its maximum flow value. Maximum flow is normally measured at a low head and does not represent the actual operating point.

4. Calculate the Total Required Head

The required pump head is determined by the total resistance of the circulation system.

The calculation should include pressure losses through:

• Straight pipes
• Bends and fittings
• Control valves
• Filters and strainers
• Heat exchangers
• Heaters
• Mold channels
• Production equipment
• Other restrictions in the circulation circuit

Liquid viscosity also affects pressure loss. A thermal oil system may require more pump head during cold startup because the oil is more viscous at lower temperatures.

Select the pump according to the required flow at the required head, rather than considering maximum flow and maximum head as simultaneous values.

5. Check the Pump Performance Curve

The pump performance curve shows the relationship between flow and head. The required operating point should fall within a stable and efficient section of the curve.

When reviewing a performance curve:

1. Locate the required flow rate.
2. Confirm the available head at that flow.
3. Check the motor power requirement.
4. Consider changes in liquid viscosity.
5. Allow a reasonable operating margin.
6. Avoid excessive oversizing.

An oversized pump may create unnecessary pressure, energy consumption, noise and component wear. An undersized pump may not provide enough circulation for stable temperature control.

6. Consider Liquid Viscosity at Startup

Viscosity is especially important in thermal oil systems. As temperature decreases, some oils become more viscous and require more power to circulate.

The motor and pump should be evaluated for the cold-start condition as well as normal operation. A pump that performs correctly with hot oil may experience higher load when starting with cold oil.

Provide the following information where possible:

• Oil brand and grade
• Viscosity at startup temperature
• Viscosity at operating temperature
• Liquid density
• Minimum startup temperature
• Maximum operating temperature

7. Select Compatible Pump Materials

High temperature can change the mechanical strength, corrosion resistance and dimensional stability of pump materials.

Material selection should consider:

• Liquid composition
• Operating temperature
• System pressure
• Corrosion risk
• Cleanliness requirements
• Thermal expansion
• Expected service life

Stainless steel is used for many industrial liquids, but not every stainless steel grade is compatible with every chemical. Internal bearings, gaskets, seals and other wetted components must also be checked.

8. Choose the Appropriate Sealing Structure

Mechanical Seal Pump

A mechanical seal pump uses a rotating shaft and seal faces to control leakage. The seal faces, elastomers and cooling arrangement must be suitable for the temperature, pressure and liquid.

Mechanical seals are replaceable and familiar to many maintenance teams, but wear or unsuitable operating conditions may eventually cause leakage.

Magnetic Drive Pump

A magnetic drive pump transfers motor power through magnetic coupling and does not use a conventional rotating shaft seal.

This design can reduce leakage risk from the shaft-seal area and may be considered for clean thermal oil, corrosive liquids and applications where fluid containment is important.

Magnetic drive pumps generally require clean liquid, correct internal circulation and protection against dry running. Magnet, bearing and containment-shell materials must be suitable for the maximum temperature.

9. Check System Pressure and Vapor Conditions

Operating pressure and pump head are related, but they are not the same specification. Confirm both the normal system pressure and maximum allowable pressure.

For hot-water systems, sufficient pressure may be necessary to prevent the water from boiling at the operating temperature.

If pressure at the pump inlet is too low, the liquid may vaporize locally and cause cavitation. Cavitation can result in:

• Noise and vibration
• Unstable flow
• Reduced pump performance
• Damage to the impeller and internal components

The suction pipe should provide adequate inlet pressure under the maximum-temperature operating condition.

10. Design the Suction Piping Correctly

Good suction piping helps the pump operate reliably.

Recommended considerations include:

• Keep the suction pipe as short and direct as practical.
• Avoid unnecessary bends and restrictions.
• Use an appropriate pipe diameter.
• Prevent air from entering the system.
• Ensure the pump is filled before startup.
• Install and clean strainers correctly.
• Avoid placing a throttling valve in a way that restricts the pump inlet.

Actual piping requirements depend on the system design and pump type.

11. Confirm Voltage, Frequency and Motor Requirements

Electrical requirements vary by country and installation.

Before ordering, confirm:

• Single-phase or three-phase power
• Rated voltage
• Frequency
• Required motor power
• Motor protection level
• Indoor or outdoor installation
• Ambient temperature
• Applicable local electrical standards

The motor should have sufficient power for the actual liquid viscosity and operating conditions.

Information Required for Pump Selection

Common High-Temperature Pump Selection Mistakes

• Providing only the normal temperature and not the maximum temperature
• Selecting a pump only by motor power
• Comparing only maximum flow
• Ignoring the required head
• Ignoring cold-start oil viscosity
• Using unsuitable seals, bearings or gasket materials
• Failing to check chemical compatibility
• Restricting the suction pipe
• Operating the pump without liquid
• Ordering the wrong voltage or frequency

High-Temperature Pump Support from FENGHE

Fuzhou Fenghe Machinery Co., Ltd. supplies FENGHE industrial circulation pumps for temperature-control, hot-water, thermal-oil and related industrial systems.

Each pump configuration should be evaluated according to the actual liquid, operating temperature, required flow, required head, system pressure, connection size and electrical supply.

OEM and wholesale inquiries from equipment manufacturers, importers, distributors and industrial service companies are welcome.

Website: www.fzfenghe.com
Email: info@meccpower.com

Frequently Asked Questions

Can a standard water pump be used for high-temperature liquid?

Not necessarily. The casing, bearings, seal, gaskets, motor and other components must be suitable for the actual maximum temperature and pumped liquid.

What temperature should I provide to the supplier?

Provide the normal continuous temperature, maximum possible temperature and cold-start temperature if thermal oil is used.

Why is thermal oil viscosity important?

Thermal oil may become more viscous at lower temperatures. Higher viscosity can reduce pump performance and increase the required motor power during startup.

Should I select a pump by its maximum flow?

No. Select the pump according to the required flow at the required head and verify the operating point on the performance curve.

Is a magnetic drive pump suitable for high-temperature circulation?

It may be suitable when its magnets, bearings, casing and internal components are rated for the liquid and maximum temperature. Dry-running protection and clean-liquid conditions may also be required.

What if I do not know the required head?

Provide the pipe length, pipe diameter, height difference, fittings, valves, equipment resistance, liquid viscosity and required flow for preliminary evaluation.

Need help selecting a high-temperature circulation pump? Please contact FENGHE with the liquid type, operating temperature, required flow rate, head, voltage and frequency for pump selection support.