Inline Water Pump

Inline Water Pump

What is an inline water pump?

An inline water pump is a type of centrifugal pump whose suction and discharge nozzles rest in a straight line of piping and are connected inside the pump casing. These pumps are designed to operate with water as the fluid medium. The pump consists of impeller(s), electric motor, and casing. The inline water pump can be driven using an electric motor, a turbine, or a diesel engine. The flow of water through an inline pump does not vary. The pumps are mostly used for domestic and residential building applications including water supply systems, water heating, and circulation systems, water pumping among others.

Inline water pump with an AC induction motor

An inline water pump may come in either vertical or horizontal configurations. The horizontal inline water pump has a horizontally oriented shaft while the vertical inline water pump has a vertically oriented shaft. The design of the inline water pump is normally compact and the pump has less space requirement compared to other large types of pumps. Most inline pumps, however, lack the self-priming ability.

How does an inline water pump work?

The working of an inline water pump is based on the principle of the forced vortex, which states that when a mass of fluid rotates due to an applied force, the pressure head of the fluid increases. The resulting increase in pressure head leads to the transfer of the fluid from one reservoir to the desired location. The operation of an inline water pump follows the steps below

  1. Before starting, the pump casing is first filled with the liquid to be transferred- a process known as pump priming.
  2. The inline pump rotor is then mechanically powered using an electric motor. The impeller is directly coupled to the electric motor via a shaft and it turns at the same motor rpm.
  3. When the pump’s impeller begins rotating, a vacuum is created inside the impeller’s eye and the liquid is drawn toward the center of the impeller in the axial direction.
  4. Once the water strikes the blades of the impeller, the centrifugal force acting on the blades rotates the water radially and axially outwards until it passes through all of the impeller components.
  5. The impeller blades impart kinetic energy on the fluid and accelerate it toward the pump casing.
  6. In the pump volute, the speed of the water gradually decreases while the pressure increases due to the conversion of the kinetic energy of water into the pressure head. Finally, the fluid achieves the desired pressure and pumps to the desired location.

Applications of inline water pump

Inline water pumps find applications in the following areas:

  • Water heating and circulation systems

This is because the pump cans withstand high temperatures

  • Water supply systems
  • Irrigation
  • Pumping water
  • supporting industrial fire protection equipment
  • Regulation of hot water
  • Boiler feed pumps

Advantages of inline water pump

  • Inline water pumps are highly reliable and efficient
  • Inline water pumps Low Net Positive Suction Head (NPSH)

A low NPHS minimizes the suction pressure that is required to feed the pump and makes water flow through the pump easily.

  • Space-saving

The inline water pump’s suction and discharge nozzles are in line with each other hence the pump has small space requirements.

  • The inline water pump can run without seals under low flow conditions
  • They can operate in high-thermal and pressure applications
  • The inline water pump is easy to install and maintain
  • The inline water pump provides steady and consistent output
  • They have low operational cost

Disadvantages of inline water pump

  • Inline water pumps cannot self-prime; hence initial manual priming must be carried out at the initial pump start-up.
  • Not suitable for water containing suspended particles
  • Inline water pumps are susceptible to corrosion due to seal leakage in the pump casing. Corrosion can potentially cause damage to the pump.
  • sometimes the pump may overheat
  • A vertical inline water pump has unequal weight distribution and most of the pump weight is concentrated below the pump casing.
  • Entrained gases in the water may accumulate within the seal chamber leading to the failure of mechanical seals.

Selection of inline water pump

The selection of an inline water pump for a particular application should be based on proper consideration of various factors affecting the performance and efficiency of the pump. Such factors include the following.

The power supply

Your power supply is a key thing to consider before purchasing inline water pump for your application. The supply power should be equal to the pump’s rated power, which is usually indicated on the pump nameplate. In industrial pump applications, pump power refers to the amount of energy needed to move liquid from the suction side to the discharge side of the pump. The supply power to the inlet water pump should be sufficient to achieve the required fluid pressure head and flow rate. The amount of power is usually expressed in terms of Horse Power (HP).

Inline pump design

The pump design is an important factor to consider especially when the installation space is limited. The inline pump has both vertical and horizontal design configurations, depending on the pump shaft orientation. The horizontal inline pump requires a large installation space compared to the vertical inline water pump. Unlike the vertical inline water pump, the horizontal inline water allows the operation of the pump using a motor, a turbine, or an engine. However, the vertical configuration requires relatively small installation space, and it is more suitable for high-pressure applications as compared to the horizontal inline water pump. Therefore, the best pump selection for your application should be based on proper examination of the pump characteristics against the specific application requirements.

Number of pump stages

Inline pump manufacturers avail both single and multistage inline pumps. Multistage inline water pumps are best suited for applications involving high pressure. For example, as a booster pump for pressurizing fluids. On the other hand, a single-stage inline pump mostly applies in the transfer of more direct flow and low-pressure fluids. So, based on the pressure requirement of your application you can decide on whether to go for a single-stage or multi-stage inline water pump.

The pump’s flow rate

The pump flow rate is the amount of fluid that is being transferred by the pump per unit of time. It is usually expressed in units of volume per minute or gallon per minute (GPM). The right pump should be able to meet the desired flow rate for that particular application.

Head requirement

In fluid mechanics, the pump head can be defined as the height to which a pump can pressurize the fluid. The maximum head of the inline water pump is the height at which the pump’s flow rate becomes zero. The head is measured in feet. To determine your pump head requirement, consider the distance between the water reservoir and the point to which you water to pump water, or the height of your building. The choice of the inline water pump should be able to raise the water to that height. In most cases, inline water pumps can meet high-pressure head requirements. However, it is a good practice to counter-check the pump head against your specific requirements.

Design of the end flanges

The inline water pump’s flanges should be designed for ease of installation. They should be able to fit and align perfectly while taking the minimum time possible. The ease of installation contributes towards reducing the initial installation and operation cost of the inline water pump. Generally, the pump flanges should be able to meet the ANSI and API design standards.

Cost of the inline water pump

Inline pump manufacturers avail a wide range of inline water pumps with diverse performance metrics and prices. Depending on your budget, you can select the best pump that offers you the best performance for your application.

Inline pump troubleshooting

The inline pump gives zero flow after startup

  • The inline water pump operating in reverse (Ensure that the motor rotates in the direction indicated by the arrow on the pump casing; the direction of rotation can be changed by reversing the motor polarities)
  • Air in the inline water pump or suction pipework (fill the pump with water to drive out air from the pump system)
  • Suction lift is too high (lower the static lift, inspect for inlet obstruction)
  • Impeller, strainer, or check vale clogged (inspect; clean)
  • Insufficient monomeric head (use large diameter pumps, increase the pump power)

Inline water pump’s bearings overheating

  • Poor coupling alignment (check and realign)
  • The inline water pump is excessive greased (drain excess grease)
  • The inline water pump is insufficiently lubricated or lubricating oil is contaminated with dirt (inspect the level of oil or grease, clean the bearing casing and lubricate)
  • The pump’s bearing covers are fixed too tightly (loosen the bearing covers)

Inlet pump experiencing excessive vibration

  • Presence of foreign material in the inline water pump (disassemble the pump and clean)
  • The mounting plate and the foundation lacks sufficient rigidity (reinforce the foundation, mount the pump tightly)
  • The inline water pump impeller is partially clogged (clean the impeller)
  • The impeller is severely worn out (replace impeller)
  • oblique or unbalanced shaft (check shaft and replace or balance as required)
  • poor coupling alignment (inspect; align)

The pump does not develop pressure

  • The discharge line of the inline water pump is closed and priming air can’t find the way out (open the discharge line)
  • lack of priming water in the casing (fill pump casing with water at the initial start-up)
  • Leakage in mechanical seals of the inline water pump (replace seals)
  • leakage in foot valve or check valve (replace the valves)


The inline water pump article provides a detailed review of the inline water pump, the principle of operation, typical applications, advantages, and disadvantages. It also guides on the selection criteria for an inline pump and the methods of troubleshooting various common issues about the pump.

The inline water pump is a type of centrifugal pump with both suction and discharge nozzles resting in a straight line of piping and connected inside a pump casing. The pump mainly operates with water as the fluid medium. Inline water pumps are characterized by a non-variable flow of water through the pump casing, compact design, steady and consistent output. The inline water pump has several types and design configurations including the vertical inline water pump, horizontal inline water pump, single-stage and multistage inline water pumps designs. The inline water pumps are used for domestic and industrial applications such as pumping of water, water heating and circulation system, irrigation, support for industrial fire protection equipment, and many more.

These pumps are highly preferred because of the many benefits they offer in different applications. Such benefits include high reliability and efficiency, low net positive head requirement, space-saving, easy installation and maintenance, steady and consistent output, and low cost of operation. The inline water pumps, however, do share some common limitations of the centrifugal pumps such as inability to self-prime, susceptibility to corrosion, overheating. These pumps are also not suitable for pumping water containing solid particles. Sometimes the entrained gases in the water may also accumulate within the seal chamber leading to the failure of mechanical seals. To make the best choice of inline water pump, from the wide varieties of the pumps available in the market, one needs to consider the type of pump, cost of the pump, flow rate, and head requirements for the application.