Understanding the Different Types of Screw Pump Accessories

2026-04-13 05:41:58

Understanding the Different Types of Screw Pump Accessories

Screw pumps are widely used in oil & gas, petrochemical, power generation, marine, food, and general industrial

applications. A key factor in screw pump reliability and efficiency is the correct selection and configuration of

screw pump accessories. This guide explains the different types of screw pump accessories, their functions, typical

specifications, and how they affect system performance.

1. What Are Screw Pump Accessories?

Screw pump accessories are auxiliary components installed around the pump to improve safety, reliability, process

control, ease of maintenance, and energy efficiency. While the screw pump itself includes the casing, rotors, shaft,

and bearings, accessories include items such as mechanical seals, couplings, strainers, relief valves, baseplates,

instrumentation, and piping components.

In many engineering specifications (including API 676 for rotary positive displacement pumps), screw pump accessories

are treated as part of the complete pump package. Selecting the right accessories is often as important as selecting

the correct pump type (single screw, twin screw, triple screw) and pump size.

1.1 Common Objectives of Screw Pump Accessories

• Protecting the pump from damage due to dry running, cavitation, or overpressure

• Ensuring leakage control and compliance with environmental standards

• Reducing vibration and noise transmitted to the structure

• Improving ease of alignment, installation, and maintenance

• Ensuring accurate flow, pressure, and temperature monitoring

• Optimizing energy consumption and system efficiency

1.2 Overview of Main Accessory Categories

The most common screw pump accessory groups include:

• Sealing systems (mechanical seals, packing, seal support systems)

• Shaft couplings and drive accessories

• Baseplates, skids, and mounting systems

• Suction strainers, filters, and air eliminators

• Valves and safety devices (relief valves, check valves, isolation valves)

• Piping accessories (expansion joints, reducers, flexible hoses)

• Instrumentation and monitoring devices

• Heating, cooling, and thermal management accessories

• Lubrication and flushing systems

• Electrical and control accessories (VFDs, soft starters, panels)

2. Sealing Accessories for Screw Pumps

Reliable shaft sealing is critical for screw pumps, especially when handling hazardous, corrosive, or valuable fluids.

The main sealing accessories are packing seals, mechanical seals, and seal support systems.

2.1 Gland Packing (Soft Packing)

Gland packing uses braided rings of soft material compressed around the shaft or sleeve. It is simple and robust, mainly

used for non-hazardous fluids and moderate pressures.

Advantages of Gland Packing

• Low initial cost and simple installation

• Tolerant of shaft deflection and misalignment

• Easy to adjust or replace in the field

Limitations of Gland Packing

• Requires continuous leakage for lubrication and cooling

• Higher friction and energy consumption

• Not suitable for strict environmental regulations

Typical Packing Materials

• PTFE and PTFE/graphite blends

• Graphite and carbon fiber

• Aramid fiber and synthetic fibers

2.2 Mechanical Seals

Mechanical seals are the most common sealing solution for modern screw pumps. They provide reliable, controlled leakage

and can meet environmental emission standards. Mechanical seal selection for screw pumps depends on pressure, speed,

fluid properties, and safety requirements.

Types of Mechanical Seals Used with Screw Pumps

• Single mechanical seals – Basic sealing for clean, non-hazardous liquids

• Double mechanical seals (tandem or back-to-back) – For hazardous, toxic, or abrasive media

• Cartridge seals – Pre-assembled units for easier installation and improved reliability

• Balanced seals – For higher pressures and reduced face loading

Common Mechanical Seal Face Materials

• Carbon vs. Silicon Carbide (SiC)

• Carbon vs. Tungsten Carbide (TC)

• SiC vs. SiC for abrasive or corrosive fluids

• TC vs. TC for high-pressure, high-load applications

2.3 Seal Support Systems (Seal Plans)

For double mechanical seals or demanding services, seal support systems provide flushing, cooling, or pressurization to

extend seal life. These accessories are especially relevant for screw pumps handling viscous, polymerizing, or abrasive

fluids.

Typical Seal Support Functions

• Provide clean barrier or buffer fluid

• Maintain positive pressure differential to process fluid

• Remove heat generated at the seal faces

• Prevent solidification or crystallization around seal faces

Common Seal Support Components

• Seal pots / reservoirs with level gauge

• Heat exchangers or cooling coils

• Pressure and temperature gauges

• Flow indicators and orifices

• Piping and fittings according to standardized seal plans

3. Couplings and Drive Accessories for Screw Pumps

Couplings connect the screw pump shaft to the driver (usually an electric motor, but sometimes a diesel engine or

turbine). Correct coupling selection minimizes vibration, misalignment, and maintenance needs.

3.1 Types of Shaft Couplings Used with Screw Pumps

• Flexible jaw couplings – For general industrial screw pumps, moderate torque, and misalignment.

• Gear couplings – For high torque and demanding conditions, common in heavy industry.

• Disc couplings – For high-speed screw pumps requiring precise alignment and low backlash.

• Elastomeric couplings – To absorb shock loads and dampen torsional vibration.

• Spacer couplings – Provide space to remove mechanical seals without disturbing the motor.

3.2 Key Coupling Selection Parameters

• Rated torque and peak torque

• Misalignment capacity (angular, parallel, axial)

• Maximum rotational speed

• Temperature range and chemical resistance of flexible elements

• Compliance with industry standards and safety factors

3.3 Coupling Guards and Safety Accessories

Coupling guards are essential safety accessories, preventing personnel from contacting rotating parts. Typical features

include:

• Metal or composite construction with ventilation openings

• Compliance with local machine safety regulations

• Removable sections for inspection and maintenance

• Integrated nameplates and warning labels

4. Baseplates, Skids, and Mounting Accessories

Screw pump performance depends strongly on proper alignment and rigid mounting. Baseplates and skids are essential

accessories that support the pump, driver, and sometimes additional equipment such as filters and control panels.

4.1 Baseplates

A baseplate is a fabricated steel or cast-iron structure onto which the screw pump and motor are mounted. It ensures

stable alignment, allows for grouting, and distributes loads to the foundation.

Common Baseplate Features

• Machined mounting pads for pump and motor

• Alignment jackscrews and hold-down bolts

• Open or closed channel construction

• Provision for grout holes and drainage

• Corrosion-resistant coatings

4.2 Skid-Mounted Screw Pump Packages

Skid-mounted units integrate pump, driver, base, and sometimes suction strainers, filters, valves, and instrumentation

on a single structural frame. Skids are common in oil & gas, marine, and power plant installations.

Advantages of Skid-Mounted Screw Pump Systems

• Factory alignment and testing before shipment

• Reduced on-site installation time and cost

• Compact layout and easy relocation

• Centralized piping and wiring interfaces

4.3 Vibration Isolation Accessories

To reduce vibration transfer and noise, screw pump systems may include:

• Resilient mounting pads or anti-vibration mounts

• Inertia bases for sensitive installations

• Grouted baseplates with proper chocking

5. Suction Strainers, Filters, and Air Elimination Accessories

Clean suction conditions are critical for screw pump reliability. Solid particles, debris, and entrained air can cause

wear, cavitation-like phenomena, and performance loss. Filtration and air elimination accessories mitigate these risks.

5.1 Suction Strainers and Baskets

Suction strainers are installed on the pump suction line or inside the reservoir to capture coarse particles. Types

include:

• Y-strainers – Inline units with mesh screens, suitable for small to medium screw pumps.

• Basket strainers – Larger capacity for higher flow or dirty services.

• Foot valves with strainers – For vertical suction lines or tank bottom suction.

5.2 Line Filters and Fine Filtration

For high-precision screw pumps or systems sensitive to particulate contamination (such as hydraulic or lubrication

systems), fine filters with replaceable elements are installed either on the suction or discharge side.

Key Filter Parameters

• Filtration rating (e.g., 10 μm, 25 μm, 40 μm)

• Dirt-holding capacity and pressure drop

• Bypass valve setting

• Element material and collapse pressure

5.3 Air Eliminators and Degassing Accessories

Entrained air or gas in the suction line can severely reduce screw pump efficiency and cause noise and vibration.

Accessories for air elimination include:

• Air release valves on high points of the suction line

• Degassing chambers or air separators upstream of the pump

• Tank design features that promote natural air separation

6. Valves and Safety Accessories for Screw Pumps

Because screw pumps are positive displacement pumps, overpressure protection is essential. Valves and safety accessories

regulate flow, prevent backflow, and protect the pump and piping.

6.1 Relief Valves (Safety Valves)

Relief valves are mandatory accessories for screw pump systems. They open when discharge pressure exceeds a preset

value, bypassing flow back to the suction or to a tank, and thus limiting system pressure.

Types of Relief Valves

• Integral relief valves – Built into the pump casing for compact protection.

• External relief valves – Installed on discharge piping, allow flexible setting and maintenance.

• Direct-acting spring-loaded valves – Simple, fast response, common in most installations.

6.2 Check Valves (Non-Return Valves)

Check valves prevent reverse flow through the screw pump during shutdown or backpressure events. They protect the pump

from reverse rotation and mechanical damage.

Common Check Valve Types

• Swing check valves

• Piston or lift check valves

• Dual-plate or wafer check valves for compact installations

6.3 Isolation Valves

Isolation valves such as gate valves, ball valves, or butterfly valves allow the pump to be disconnected from the system

for maintenance. They are typically installed on both suction and discharge sides.

7. Piping Accessories Around Screw Pumps

Screw pump piping accessories ensure smooth flow into and out of the pump and help to manage thermal expansion and

structural loads. Good piping design and accessory selection are crucial for long-term reliability.

7.1 Flexible Connectors and Expansion Joints

Flexible connectors reduce the transmission of vibration from the pump to the piping and absorb thermal expansion.

Typical options include:

• Rubber expansion joints for low to medium pressure and temperature

• Metal bellows expansion joints for high temperature or pressure services

• Fabric expansion joints for low-pressure, large duct work

7.2 Reducers and Pipe Fittings

Smooth transitions between pump nozzles and piping minimize pressure losses and turbulence.

• Concentric reducers on vertical lines

• Eccentric reducers on horizontal suction lines (flat side on top) to avoid air pockets

• Long-radius elbows upstream of the pump when direction changes are necessary

7.3 Pulsation Dampeners and Accumulators

Although screw pumps generally produce low pulsation compared with other positive displacement pumps, certain

applications (especially at low speed or high differential pressure) can benefit from pulsation dampeners or

accumulators to stabilize flow and protect instrumentation.

8. Instrumentation and Monitoring Accessories for Screw Pumps

Instrumentation allows operators to monitor screw pump performance, detect faults early, and optimize operation.

Monitoring accessories range from simple gauges to fully integrated digital condition monitoring systems.

8.1 Pressure Measurement Accessories

Pressure gauges and transmitters are typically installed on:

• Suction line, near pump inlet

• Discharge line, close to pump outlet

• Seal support systems and lubrication circuits

Common Pressure Instrument Features

• Bourdon tube gauges for local indication

• Electronic transmitters with 4–20 mA or digital outputs

• Pressure switches for interlocks and alarms

8.2 Temperature Measurement Accessories

Temperature sensors protect screw pumps from overheating and provide information about fluid viscosity and thermal

conditions.

• RTDs or thermocouples on bearing housings

• Thermowells on suction and discharge lines

• Temperature switches for alarm and trip functions

8.3 Flow Measurement Accessories

Because screw pumps deliver nearly constant volumetric flow, flow meters are often used for process control and energy

management. Typical options include:

• Positive displacement flowmeters for accurate measurement at low flow

• Coriolis mass flowmeters for high-accuracy and density-compensated readings

• Electromagnetic flowmeters for conductive liquids

8.4 Vibration and Condition Monitoring Accessories

Advanced screw pump installations may include:

• Vibration sensors on pump bearings and baseplate

• Online condition monitoring systems with trend analysis

• Wireless sensors for retrofit applications

9. Heating, Cooling, and Thermal Management Accessories

Many screw pumps handle viscous fluids such as heavy fuel oil, bitumen, lubricating oil, and polymers. Maintaining the

correct fluid temperature is essential to keep viscosity within the pump's optimum range. Thermal management accessories

are therefore a crucial part of screw pump systems.

9.1 Heating Jackets and Tracing

Heating jackets are welded or cast around the pump casing and sometimes the suction/discharge covers, allowing steam,

thermal oil, or hot water to circulate and heat the fluid inside the pump.

Key Features of Heating Jackets

• Designed for specific heating medium and pressure

• Uniform heating to avoid localized hot spots

• Complementary to external piping heat tracing

Heat tracing (steam or electric) is often applied to suction and discharge piping, valves, and accessories to maintain

consistent temperature throughout the system.

9.2 Cooling Coils, Fans, and Heat Exchangers

Cooling may be required for:

• Bearings and lubrication oil in high-speed screw pumps

• Mechanical seals in high-temperature or high-pressure service

• Hydraulic fluid in variable speed drive systems

Common cooling accessories include:

• Oil-to-air or oil-to-water heat exchangers

• Cooling jackets or coils in bearing housings

• Motor-mounted fans or forced air cooling systems

10. Lubrication and Flushing Accessories for Screw Pumps

Proper lubrication is essential for screw pump bearings, timing gears (in twin screw pumps), and sometimes the screws

themselves when operating as lubricated pumps. Flushing accessories help keep seals and internal surfaces clean.

10.1 Bearing and Gearbox Lubrication Systems

Lubrication accessories may include:

• Oil sumps with level gauges and breathers

• Built-in or external lubrication pumps

• Oil filters and coolers in circulation systems

• Grease fittings for greased bearings

10.2 Seal Flushing and Quenching Systems

Mechanical seal performance can be improved by flushing clean fluid across the seal faces or quenching the atmospheric

side. Accessories may include:

• Flush lines from discharge to seal chamber with orifice restriction

• External flush supply units for particularly dirty or hot processes

• Quench connections for steam or nitrogen purging

11. Electrical and Control Accessories for Screw Pumps

Electrical and control accessories allow screw pumps to operate safely and efficiently within process requirements.

These accessories integrate the pump with plant automation systems.

11.1 Variable Frequency Drives (VFDs)

Screw pumps often benefit from variable speed operation, especially when handling variable flow rates or pressures.

VFDs are commonly used to:

• Match pump capacity to process demand

• Reduce energy consumption

• Provide soft start and stop to minimize mechanical stress

• Implement pressure or flow control loops

11.2 Motor Starters and Protection Relays

Motor control centers and local starters provide:

• Overload and short-circuit protection

• Phase loss and phase imbalance monitoring

• Emergency stop functions

• Integration with process interlocks (low suction pressure, high temperature, etc.)

11.3 Local Control Panels and HMI

Local control panels for screw pumps may include:

• Start/stop buttons and selector switches

• Status lights and alarms

• Analog or digital indicators for key process variables

• Human-machine interfaces (HMI) for advanced pump packages

12. Materials and Surface Treatment for Screw Pump Accessories

The choice of materials and surface treatment for screw pump accessories must consider fluid properties, temperature,

pressure, and environmental conditions.

12.1 Common Materials for Screw Pump Accessories

• Carbon steel – Widely used for baseplates, skids, and general piping accessories.

• Stainless steel (304, 316, duplex) – For corrosion resistance in aggressive or hygienic services.

• Bronze and brass – For seawater, marine, and some lubricating services.

• Alloy steels – For high-pressure or high-temperature environments.

• Elastomers – Used in gaskets, seals, flexible connectors (EPDM, NBR, FKM, PTFE-based compounds).

12.2 Surface Coatings and Treatments

Surface treatments protect accessories from corrosion and wear:

• Epoxy coatings for baseplates and steel structures

• Hot-dip galvanizing for outdoor installations

• Nickel or chrome plating for specific small accessories

• Rubber or polymer linings for erosion and corrosion resistant internals

13. Accessory Selection Considerations for Screw Pump Systems

Selecting screw pump accessories involves balancing technical requirements, cost, maintenance, and safety. The following

considerations are helpful for engineers and designers.

13.1 Process Conditions

• Fluid properties: viscosity, temperature, density, corrosiveness, toxicity

• Operating pressure and differential pressure

• Required flow range and turndown

• Presence of solids, gas, or entrained air

13.2 Reliability and Maintenance Strategy

• Required mean time between failures (MTBF)

• Planned maintenance intervals and spare parts strategy

• Availability of skilled technicians for complex accessories (e.g., seal systems, VFDs)

13.3 Regulatory and Environmental Requirements

• Emission limits and environmental regulations

• Health and safety standards for rotating equipment

• Industry-specific guidelines for materials and designs

13.4 Cost of Ownership

While basic accessories may reduce initial investment, advanced screw pump accessories (such as double seals, condition

monitoring, or high-efficiency drives) can significantly reduce the total cost of ownership over the life of the system.

14. Example Screw Pump Accessory Configuration

The following table illustrates a typical configuration of screw pump accessories for an industrial lubricating oil

system. This example is generic and intended to highlight how different accessories work together.

15. Conclusion: Maximizing Screw Pump Performance with the Right Accessories

Understanding the different types of screw pump accessories is essential for designing safe, efficient, and reliable

pumping systems. From sealing solutions and couplings to filters, valves, and instrumentation, each accessory plays a

specific role in protecting the pump and ensuring continuous operation.

When selecting screw pump accessories, engineers should consider process conditions, reliability targets, regulatory

requirements, and total cost of ownership. Applying best practices in accessory selection leads to longer pump life,

reduced downtime, and optimized energy usage across a wide range of screw pump applications.

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