Types of valves and pumps used in chemical process systems

Understanding the role of valves and pumps

The main types of valves and pumps in chemical process systems are best compared by function. Pumps add energy to move liquids through piping. Valves start, stop, throttle, isolate, relieve, or redirect that flow. In many plants, centrifugal pumps handle clean, low-to-medium-viscosity transfer duties, while positive displacement pumps are used for metering, viscous liquids, and services that need nearly fixed flow. For valves, gate, ball, butterfly, globe, check, control, diaphragm, pinch, and relief valves each address a different flow-control need.

The right selection depends on more than the equipment name. Fluid properties, pressure, temperature, corrosion risk, solids content, cleanability, energy use, maintenance access, and safety requirements all affect the choice. For engineers, buyers, and plant teams, the practical question is which type fits the process duty without creating avoidable pressure loss, cavitation, leakage, contamination, or downtime.

Common types of pumps

Industry references such as the U.S. Department of Energy pump system guidance and Hydraulic Institute materials generally separate industrial pumps into two broad families: rotodynamic pumps and positive displacement pumps. Centrifugal pumps are the most common rotodynamic design. Positive displacement pumps include rotary and reciprocating designs that move a defined volume of liquid with each cycle.

Centrifugal pumps

A centrifugal pump uses a rotating impeller to increase liquid velocity, then converts part of that velocity into pressure. These pumps are widely used for low-viscosity chemicals, solvents, cooling water, condensate, brines, light hydrocarbons, and general transfer services.

• Typical strengths: continuous flow, relatively simple construction, a broad capacity range, and lower maintenance complexity in clean-liquid service.
• Typical limits: performance changes with system resistance, viscosity, suction conditions, and impeller wear.
• Selection focus: flow rate, total dynamic head, net positive suction head margin, material compatibility, seal design, and an operating point near the preferred efficiency region.

In chemical plants, centrifugal pumps are usually selected when the process needs steady transfer rather than exact volumetric dosing. Depending on duty and leakage-control requirements, they may be single-stage or multistage, horizontal or vertical, end-suction, in-line, split-case, canned motor, magnetic drive, or sump designs.

Positive displacement pumps

A positive displacement pump traps a fixed volume of liquid and forces it into the discharge line. This makes it useful where flow accuracy, high-viscosity handling, or high pressure at lower flow is important. Common types include gear, screw, lobe, vane, progressive cavity, piston, plunger, diaphragm, and metering pumps.

• Typical strengths: good handling of viscous fluids, more predictable flow per revolution or stroke, and suitability for dosing or high-pressure service.
• Typical limits: sensitivity to overpressure, need for pressure relief protection, pulsation in some reciprocating designs, and close attention to internal clearances and wear.
• Selection focus: viscosity, abrasiveness, shear sensitivity, suction lift, allowable pulsation, cleanability, pressure rating, and relief-valve arrangement.

Positive displacement pumps should not be treated as interchangeable with centrifugal pumps. A discharge blockage that might push a centrifugal pump toward shutoff head can create dangerous overpressure in a positive displacement system unless protective devices are installed and maintained.

Specialty pumps for chemical service

Chemical applications often add constraints beyond flow and head. Magnetic drive pumps and canned motor pumps are used where leakage reduction is critical. Air-operated double diaphragm pumps are common for drum unloading, hazardous areas, slurries, or intermittent transfer. Peristaltic pumps can isolate the liquid inside tubing, which helps with corrosive or shear-sensitive fluids, although tubing life and pressure range must be considered.

No specialty pump is universally superior. A sealless design may reduce fugitive leakage risk, but it still requires correct fluid compatibility, bearing lubrication by the process liquid, temperature control, and dry-run protection where applicable.

Common types of valves

The Valve Manufacturers Association commonly describes valves by motion and function, including linear-motion valves, quarter-turn valves, self-actuated valves, and control valves. In process plants, a valve may be chosen for isolation, throttling, non-return service, pressure protection, slurry handling, sanitary operation, or automated control.

Gate valves

Gate valves use a gate or wedge that moves into the flow path. They are mainly used for fully open or fully closed isolation. When open, many gate valve designs provide a relatively unobstructed flow path. However, they are not normally preferred for throttling because partial opening can cause vibration, seat damage, and poor control.

Globe valves

Globe valves use a plug and seat arrangement that changes the flow path inside the body. They are commonly used for throttling and manual regulation because they provide better control than gate valves. The tradeoff is usually higher pressure drop, which affects pump sizing and energy consumption.

Ball valves

Ball valves use a rotating ball with a port through it. A quarter turn opens or closes the flow path. They are popular for isolation because they operate quickly and can provide tight shutoff when properly specified. Full-port ball valves reduce restriction, while reduced-port designs may be smaller and less costly but add pressure loss.

Butterfly valves

Butterfly valves use a rotating disc in the flow path. They are compact and often economical for larger pipe sizes. They can serve isolation and some throttling duties, but disc position, seat design, pressure class, temperature, and chemical compatibility are important. High-performance butterfly valves are often used where standard resilient-seated designs are not suitable.

Check valves

Check valves are self-actuated valves designed to reduce reverse flow. Swing, lift, dual-plate, ball, and nozzle check valves each respond differently to flow velocity and pressure changes. Incorrect sizing can lead to chatter, slam, water hammer, or premature wear, so check valves should be selected for actual flow conditions rather than line size alone.

Diaphragm and pinch valves

Diaphragm valves use a flexible diaphragm to isolate the process fluid from many working parts. They are often considered for corrosive fluids, clean service, and applications where leak paths must be minimized. Pinch valves use a flexible sleeve that closes by compression, making them useful for slurries or fluids with suspended solids. Their limits include sleeve or diaphragm material compatibility, pressure, temperature, and cycling life.

Relief and safety valves

Pressure relief valves and safety valves protect equipment and piping against overpressure. They are not normal control valves and should not be used as routine throttling devices. In chemical service, relief devices require careful sizing, set pressure selection, discharge routing, and inspection planning according to the applicable code and plant safety basis.

How pump and valve choices affect each other

Pumps and valves are often purchased as separate components, but they operate as one hydraulic system. A valve that adds unnecessary restriction can move a centrifugal pump away from its efficient operating range. A pump that produces more pressure than the valve trim can tolerate may cause erosion, noise, flashing, cavitation, or control instability. See also: Storage Systems.

System need	Common pump direction	Common valve direction	Main caution
Clean liquid transfer	Centrifugal pump	Ball, butterfly, gate, or check valves	Confirm suction conditions and pressure drop
Accurate chemical dosing	Metering or diaphragm pump	Check, isolation, calibration, and relief valves	Manage pulsation and overpressure
Viscous resin or polymer	Gear, screw, or progressive cavity pump	Full-port isolation and suitable relief valve	Avoid excessive shear and pressure rise
Slurry or solids-bearing liquid	Slurry-rated centrifugal or positive displacement pump	Pinch, knife gate, or abrasion-resistant valves	Account for erosion, settling, and blockage
Automated flow control	Pump selected for stable operating range	Control valve with suitable trim and actuator	Verify control valve authority, noise, and cavitation risk

A useful starting point is to compare pressure drop and control purpose before specifying valves. A ball valve may be excellent for isolation but poor for fine control. A globe valve may control well but require more pump head. A butterfly valve may save space on a large line but may not fit every chemical, temperature, or shutoff requirement.

Selection factors for chemical process duties

Choosing among the many types of valves and pumps starts with the process data sheet. The same nominal size, pressure class, or material name does not guarantee equivalent performance.

• Fluid properties: density, viscosity, vapor pressure, solids content, corrosiveness, toxicity, flammability, crystallization tendency, and temperature range.
• Hydraulic duty: normal, minimum, and maximum flow; suction pressure; discharge pressure; static lift; pipe losses; and expected operating variations.
• Materials: wetted metals, elastomers, coatings, gaskets, seats, sleeves, diaphragms, and mechanical seal materials must match the chemical environment.
• Safety: hazardous fluids may require sealless pumps, double mechanical seals, containment, pressure relief, leak detection, or fail-safe valve action.
• Energy and lifecycle cost: the U.S. Department of Energy has long emphasized that pumping system performance depends on the whole system, not only pump efficiency. Oversizing, throttling losses, poor control strategy, and neglected maintenance can all increase operating cost.
• Maintenance access: cartridge seals, removable valve seats, top-entry designs, drainability, spare parts availability, and isolation arrangements affect downtime.
• Standards and compliance: buyers may need to reference applicable ASME, API, ISO, Hydraulic Institute, or plant-specific standards depending on industry, jurisdiction, and service severity.

For more equipment guides in this topic area, visit the Pumps and Valves section.

Common selection mistakes to avoid

The first mistake is selecting by pipe size alone. A valve installed in a six-inch line is not automatically the correct six-inch valve for the duty. Flow velocity, pressure drop, shutoff class, control range, and media behavior may point to another design or trim.

The second mistake is treating rated capacity as operating capacity. Pump curves, viscosity corrections, suction conditions, and system curves determine actual performance. A pump that looks adequate at nominal flow may perform poorly if the liquid is more viscous than expected or if suction losses are underestimated.

The third mistake is using throttling as a permanent fix for oversizing. A control valve can regulate flow, but constant throttling wastes energy and may create noise, erosion, or cavitation. In many systems, impeller trimming, variable speed operation, or revised control logic may be better long-term solutions.

The fourth mistake is ignoring transient conditions. Start-up, shutdown, batch transfers, deadheading, blocked discharge, reverse flow, thermal expansion, and emergency isolation can be more demanding than steady operation. Positive displacement pumps especially require dependable pressure relief paths.

The fifth mistake is overlooking soft parts. Elastomers, seats, diaphragms, sleeves, packing, and seal faces often determine service life in chemical duties. Temperature and concentration changes can turn an otherwise acceptable material into a failure point.

Frequently asked questions

What are the two main types of pumps?

The two broad pump families are rotodynamic pumps and positive displacement pumps. Centrifugal pumps are the most common rotodynamic type. Positive displacement pumps include gear, screw, lobe, vane, piston, plunger, diaphragm, and metering designs.

Which valve is best for isolation?

Ball, gate, and butterfly valves are often used for isolation, but the right choice depends on pressure, temperature, pipe size, chemical compatibility, leakage requirements, and operating frequency. Ball valves are common for quick shutoff, while gate valves are common where full-open flow restriction must be low.

Which valve is better for throttling?

Globe valves and properly selected control valves are commonly used for throttling. Butterfly valves may also be used in some control applications. Gate valves are generally poor throttling choices because partial opening can damage seating surfaces and provide unstable control.

When should a positive displacement pump be used?

A positive displacement pump is often used for viscous liquids, accurate dosing, high-pressure low-flow service, or fluids that require a nearly fixed flow rate. The system must include suitable pressure protection because discharge blockage can create unsafe pressure rise.

Why does valve pressure drop matter when selecting a pump?

Valve pressure drop becomes part of the total system head that the pump must overcome. Excessive pressure drop can increase energy use, reduce available flow, move the pump away from efficient operation, or create control and cavitation problems.

Key takeaway

The most useful way to compare types of valves and pumps is by function, not by name alone. Pumps provide the energy to move liquid; valves determine how that liquid is isolated, controlled, protected, or redirected. In chemical process systems, the best selection balances hydraulic performance, chemical compatibility, safety, maintainability, and lifecycle cost. A clear duty definition will usually narrow the choice faster than a generic equipment list.