Triplex Pumps Explained

TRIPLEX PUMPS

EXPLAINED

HANDBOOK

First Edition, 2025

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Table of Contents

Introduction

Historical Development

Pump Components

Working Principle

Applications

Pump Type Comparison

Introduction

A triplex pump is a type of positive displacement pump that features three plungers or

pistons arranged in parallel, typically driven by a common crankshaft. This configuration

enables the pump to deliver a relatively steady flow of fluid at high pressures, making it

suitable for a wide range of industrial applications. For example, in oilfield services, high-

pressure cleaning, hydrostatic testing, and water jet cutting.

Triplex Pump

Historical Development

The triplex pump evolved from earlier single cylinder and duplex cylinder designs that were

used extensively in the 19th and early 20th centuries, particularly in the mining and oil

industries. As the demand for higher flow rates and smoother operation increased, engineers

developed the triplex configuration to reduce the magnitude of pressure pulsations on the

pump's discharge side (thus smoothing system flow), and to reduce mechanical stresses on

pump parts. The addition of a third cylinder enabled a smoother flow of fluid compared to

duplex pumps, where two cylinders are used to alternate between suction and discharge

strokes. The Triplex pumps' development aligned with advancements in materials and

machining, which allowed for more precise alignment and improved wear resistance for high-

pressure applications.

Triplex Pump (Fluid End)

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Triplex Pumps Explained | pg 1

Pump Components

A triplex pump comprises of two main sections: a power end and a fluid end. Each end contains

components that work together to convert mechanical energy into hydraulic energy.

●

Power end – houses the crankshaft, connecting rods, and bearings. The crankshaft

converts the rotary motion from the driver (usually an electric motor or combustion

engine) into reciprocating motion.

●

Fluid end – contains the cylinders, plungers, suction valves, discharge valves, and

associated manifolds; this section is directly involved in the pumping process, where

liquid is drawn-in, pressurised, and discharged.

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Triplex Pump Construction

●

Plungers – cylindrical components that move linearly within the cylinders to draw-in and

discharge fluid. They are usually made of hardened steel or ceramic-coated material to

resist abrasion and corrosion.

●

Stuffing box and seals – located between the fluid and power ends, these parts prevent

leakage of the process fluid and protect the mechanical parts from contamination.

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Triplex Pumps Explained | pg 2

●

Valves – suction and discharge non-return valves regulate fluid movement. Each valve

assembly consists of a seat, spring, and valve element (poppet or disc) designed for

reliable sealing and rapid response to pressure changes.

●

Manifolds – serve as common passages for suction and discharge flow, ensuring even

fluid distribution among the three cylinders.

●

Lubrication system – provides continuous lubrication to bearings and other moving parts,

often through splash or pressurised oil systems.

●

Cooling and flushing systems – used in high-duty or abrasive applications to maintain

operating temperature and reduce wear.

Working Principle

A triplex pump operates on the principle of reciprocating motion, where each of the three

plungers moves back-and-forth within its respective cylinder to draw-in (suction side) or

discharge fluid. The pump is typically driven by an electric motor or internal combustion

engine, via a crankshaft. The crankshaft converts the rotary motion from the driver (motor or

engine etc.) into linear reciprocating motion. The plungers are phased 120 degrees apart,

resulting in a more even distribution of forces and a reduction in pressure fluctuations on

the discharge side of the pump.

The pump incorporates suction and discharge non-return valves that open and close according

to the pressure differential created within each cylinder as the plunger moves through its suction

and discharge strokes. Each of the non-return valves (suction and discharge) is configured to

allow flow in only one direction. Suction valves allow flow into the cylinder from the suction

manifold, whilst discharge valves allow flow out of the cylinder into the discharge manifold.

Triplex Pump Plungers

On the suction stroke, the plunger moves away from the suction and discharge valves, creating a

low pressure within the cylinder. At this stage, the suction valve is open due to the pressure

differential between the cylinder and suction manifold (the suction manifold is at a higher

pressure than the cylinder). Due to the pressure differential, fluid flows from the suction

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Triplex Pumps Explained | pg 3

manifold into the cylinder. On the discharge stroke, the plunger moves towards the suction and

discharge valves, causing the suction valve to close and the discharge valve to open. Due to the

pressure differential, fluid flows from the cylinder into the discharge manifold. Springs hold the

valve elements (discs or poppets) onto their respective seats when no pressure differential

between the cylinder and suction manifold, or cylinder and discharge manifold, is present. Flow

through a valve only occurs when the pressure differential is large enough to overcome the

valve's spring tension.

Non-Return Valves (right of image)

Good to know – 'non-return valves' are also known as 'unidirectional valves', 'one-way valves',

'check valves', 'foot valves', or 'backflow preventers', depending on the industry terminology.

Applications

Triplex pumps are widely used in high-pressure applications where consistent flow and

durability are required. In the oil and gas industry, they are commonly employed for hydraulic

fracturing (fracking), acidising, cementing, and well stimulation. In industrial cleaning, triplex

pumps are utilised for high-pressure water jetting and surface preparation. Their ability to

generate pressures exceeding 10,000 psi (689 bar) makes them suitable for hydrostatic pressure

testing of pipelines and pressure vessels. In water treatment and reverse osmosis systems,

triplex pumps are used to feed high-pressure water into membrane filters.

Pump Type Comparison

Compared to centrifugal pumps, which are suitable for high-flow, low-pressure applications,

triplex pumps are preferred for low-flow, high-pressure applications. Unlike diaphragm

pumps, triplex pumps can handle abrasive, viscous, and/or high-temperature fluids with

appropriate material selection. While quintuple (five cylinder reciprocating pumps) and higher-

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Triplex Pumps Explained | pg 4

order multiplex pumps offer smoother flow with reduced pressure pulsations, they also involve

greater complexity and cost.

Quintuple Pump

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Triplex Pumps Explained | pg 5