Process pumps come in many variations: centrifugal, positive displacement, reciprocating, and rotary screw. There are also API or ANSI pumps.

This article covers not only the basics of different pump technologies but also gives a thorough explanation of reciprocating process pumps.

The Process Pump Market

In general, when industrial customers look for a process pump, they are accustomed to sourcing centrifugal pumps. This is because centrifugal pumps represent over 90% of the global pumping market. The rest of the market is covered by positive displacement pump technology, including rotary pumps (gear, vane, lobe, etc.) or reciprocating pumps.

The Process Pump Market

What Are Centrifugal Pumps?

A centrifugal pump uses centrifugal force to pump fluids. This device is designed to move fluid by means of the transfer of rotational energy from one or more driven rotors, called impellers. Fluid enters the impeller and is cast out by centrifugal force along the impeller's circumference through the vane tips.

Mechanical power is generally supplied by an electric motor. Centrifugal pumps can have efficiencies as low as 40-50 percent on low-flow/high-head service.

What Are Positive Displacement Pumps (Reciprocating Pumps)?

Positive displacement pumps (PDP) are a type of pump that captures a moving fluid in a cavity and then discharges a fixed amount of it via mechanical pressure. The displacement of fluid takes place using a plunger, piston, diaphragm, depending on the design. Some of these pumps have an expanding cavity at the suction side and a decreasing cavity at the discharge side. The liquid is sucked at the inlet side when the cavity expands and discharges when the cavity decreases.

In general, a reciprocating pump has a higher efficiency than a centrifugal pump. Reciprocating pumps operate in low-flow and high discharge pressure environments. Milton Roy’s reciprocating pumps can handle flow rates from 0.09 liters per hour to 48 cubic meters per hour, and discharge pressures of up to 1,034 bar (15,000 psi).


Milton Roy offers two different technologies of liquid ends in reciprocating pumps: packed plunger and diaphragm type.

What Is The Main Difference between Centrifugal Pumps and Reciprocating Pumps?

The main difference between centrifugal pumps and reciprocating pumps is that centrifugal pumps work with a low medium pressure head. By contrast, reciprocating pumps work with high medium pressure heads.

Reciprocating Pump vs Centrifugal Pump

Chart: Reciprocating pump vs Centrifugal pump

The Primeroy series with variable eccentric drive features a small footprint, and ensures durability and optimum performance

Primeroy Series

How to Choose The Type and Size of a Reciprocating Process Pump?

When choosing a pump, you have to take into consideration the following:

  • the technical characteristics on the flow control (listed in the table below)
  • the application
  • the total cost of ownership

The following table helps you select between a reciprocating diaphragm pump and a centrifugal pump.

reciprocating diaphragm pump and a centrifugal pump.

Note that the list of selection criteria is not exhaustive.

What Are Process Pumps?

There are two main types of process pumps: centrifugal pumps and reciprocating pumps. Both are used in oil and gas processes, refineries, the petrochemical industry, and chemical processes.

The technologies associated with process pumps are generally designed for handling any kind of fluids, but also aggressive chemical fluids.

What Are API Process Pumps?

API stands for the American Petroleum Institute which is the largest U.S. trade association for the oil and natural gas industries. It focuses on developing petroleum and petrochemical equipment and operating standards including all pump technologies.

The API has developed over 700 standards to improve safety, environmental protection, and sustainability in the oil and gas industry. These standards are adopted by many countries around the world.

Milton Roy offers a comprehensive pump range which fully complies to API 674 and API 675 standard.

  • API 674: Positive Displacement Pumps—Reciprocating
    • Piston pump / Plunger pump
    • Power pump : a reciprocating pump consisting of a power end and a liquid end connected by a frame. The power end of a power pump uses a crankshaft, connecting rods, and crossheads to transfer energy from a rotating shaft to pistons or plungers. The liquid end of a power pump consists of cylinders, pistons or plungers, and check valves.
  • API 675: Positive Displacement Pumps— Controlled Volume for Petroleum, Chemical, and Gas Industry Services
    • Packed plunger
    • PTFE diaphragm
    • Metallic diaphragm

The major advantages of API 675 pumps are:

  • To self-protect the pump and increase its reliability:
    • An integrated adjustable hydraulic pressure relief valve fully protects the drive mechanism from excessive discharge pressure.
    • An internal MARS pilot valve automatically controls the refill of the hydraulic oil.
    • The double diaphragm combined with a rupture detection system provides a leak-free solution and increases safety.
  • To control the flow rate with precision (metering modulation process) and safety margin:
    • The adjustment of the pump capacity by changing the stroke length, within a mini turn down ratio 1:10
    • The use of different worm/wheel gear ratios to change the stroking speed, in order to get the right flow rate
    • The steady accuracy within ±1% of rated flow over the specified turndown ratio 1:10
    • The linearity and repeatability within ± 3 % of rated flow over the specified turndown ratio 1:10
    • The rated capacity must be at least 110 % of the maximum capacity specified

What Are ANSI Process Pumps?

The API standard is accredited by the American National Standards Institute (ANSI)

The ANSI standard provides for dimensional interchangeability of pumps from one pump manufacturer to another.

ANSI pumps provide generally reliable service across a wide range of applications. These pumps are often used to transfer and process fluids in various industrial settings. This includes chemical plants, refineries, pulp and paper mills, and wastewater treatment plants.

API pumps are more robust and are designed for heavy duty, higher pressure, and temperature applications.

Milton Roy offers a large range of API 674 and API 675 pumps with ANSI connection. They are suitable for all processes in the oil and gas, chemical and other heavy duty industries.

Why Are Milton Roy Pumps Suitable for Your Application?

Milton Roy pumps comply with the following specifications:

Miltonroy Comprehensive range of pumps

Milton Roy has over 85 years of experience in industrial processes. We have developed a large range of options and features to cover the most critical applications such as:

  • Double diaphragm pump with a rupture detection system to offer more safety for dangerous/toxic/explosive fluids
  • Special check valves for highly viscous fluids, particles, abrasives, etc.
  • High temperature or low temperature process fluids (with or without remote check valves)
  • High suction capabilities for liquefied gasses
  • Low NPSHr design for low vapor pressure process fluids
  • Metallic diaphragm or packed plunger pumps for high discharge pressure, up to 15,000 psi – 1034 bar
  • Patented liquid end (DSD technology) for dosing a very low flow rate with high discharge pressure (0.09L/h at 130 bar – 0.03 GPH at 1885 psi)