Examining pump repair records and mean time between failures (MTBF) is of great importance for responsible and conscientious pump users. In view of this, the preface to the Pump User's Manual 2006 refers to statistics of "pump failures". For convenience, these failure statistics are often translated into MTBF (in this case, installed life before failure).[11]​.

In early 2005, Gordon Buck, John Crane Inc.'s chief engineer for field operations in Baton Rouge, Louisiana, examined the repair records of several refineries and chemical plants to obtain significant data on the reliability of centrifugal pumps. A total of 15 operating plants with nearly 15,000 pumps were included in the study. The smallest of these plants had about 100 pumps; several plants had more than 2,000. All facilities were In addition, they were considered "new", others "renovated", and others "established". Many of these plants - but not all - had an alliance contract with John Crane. In some cases, the alliance contract included the on-site presence of a technician or engineer from John Crane Inc. to coordinate various aspects of the program.

However, not all plants are refineries and results are different elsewhere. In chemical plants, pumps have historically been "throwaway" items, as chemical attack limits their useful life. Things have improved in recent years, but the somewhat restricted space available in the "old" DIN and ASME cable glands limits the type of closure that will fit. Unless the pump user upgrades the seal chamber, the pump only supports more compact and simpler versions. Without this improvement, the useful life in chemical facilities is usually between 50% and 60% of the refinery values.

Unscheduled maintenance is often one of the most significant costs of ownership, with mechanical seal and bearing failures among the leading causes. Consider the potential value of selecting pumps that cost more initially, but last much longer between repairs. The MTBF of an improved pump may be one to four years greater than that of its unimproved counterpart. It should be noted that the published average values ​​of avoided pump failures range between $2,600 and $12,000. This does not include lost opportunity costs. A fire occurs in a pump for every 1,000 breakdowns. Having fewer pump failures means having fewer destructive pump fires.

As already noted, a typical pump failure, based on actual reports from 2002, has an average cost of $5,000. This includes costs for material, parts, labor and overhead. Extending the MTBF of a pump from 12 to 18 months would save $1,667 per year, which could be greater than the cost of improving the reliability of the centrifugal pump.[11]​[12]​[13]​.

For the correct operation of rotodynamic pumps, they need to be filled with incompressible fluid, that is, liquid, since if they were filled with compressible fluid (any gas such as air) they would not work correctly.

Priming the pump consists of filling the suction pipe and the pump casing with liquid, to facilitate the suction of liquid, preventing air pockets from remaining inside. Since this operation is necessary in rotodynamic pumps, it is said that they do not have self-priming capacity. However, positive displacement pumps are self-priming, that is, even if they are filled with air, they are capable of filling the suction circuit with fluid.

In a circuit like the one shown in the attached diagram without any additional device, when the centrifugal pump stops, the fluid from the suction circuit falls into the tank, emptying the pump due to the vacuum created by the primary circuit.

The lifting height provided by the pump is always the same and responds to the following formula:

where is the delivery pressure, is the suction pressure, is the density of the fluid and is the acceleration of gravity.

Solving for the pressure difference we have:

From this formula it can be seen that the pressure difference achieved by the pump between the impulsion and the suction is greater the greater the density of the fluid to be moved.

So that for the specific case of water we have:

With which:

That is, if the pump is full of air, the suction pressure is 0.00129 times what the pump would achieve if it were full of water, that is, if it were primed. Therefore, if the pump is empty, the height that the water rises in the suction circuit above the water level in the tank is minimal and totally insufficient for the water to reach the pump.

On the other hand, operating a centrifugal pump under vacuum can damage the seal of the pump due to poor cooling since fluid does not circulate inside it, which helps to improve the dissipation of the heat produced by the pump.

Therefore, in pumping installations whose diagram coincides with that indicated in the attached diagram, an additional system is necessary to prevent the pump from depriming. Some of these systems are listed below:.

The pumps require hydraulic seals to prevent the fluids that are being driven from leaving the outside of the machine through the movement transmission path from the motor to the moving internals of the pump.

In the field of oil refining and petrochemicals there are mechanical pump seals standardized by API (American Petroleum Institute) which, although it is an American association, are applicable throughout the world. Each type of seal is called API PLAN. These seals can be single or double and, in addition, they may or may not have a cooling system.

There is also a pump seal classification according to ANSI.

Below is the API - ANSI equivalence of the most used sealing systems or plans:[14]​.

Suction pump

In a "suction pump", a cylinder containing a movable piston is connected to the water supply by a tube. A valve blocks the entry of the tube into the cylinder. The valve is like a door on hinges, which only opens upwards, letting the water rise, but not fall. Inside the piston, there is a second valve that works in the same way. When the crank is operated, the piston rises. This increases the volume under the piston, and therefore the pressure decreases. The normal air pressure acting on the surface of the water in the well forces the liquid up the tube, passing the valve—which opens—and makes it enter the cylinder. When the piston goes down, the first valve closes, and the second opens, allowing water to pass to the top of the piston and occupy the cylinder above it. The next upward stroke causes water to rise to the spigot "Spigot (valve)") and, at the same time, causes more water to enter the cylinder, below the piston. The action continues as the piston moves up and down.

A suction pump is limited action, in certain senses. It cannot provide a continuous stream of liquid or lift water over a distance greater than 10 m. between the surface of the well and the lower valve, since normal air pressure can only act with enough force to maintain a water column of that height. A booster pump overcomes these obstacles.

A type of suction pump that can lift water more than ten meters is that of the Seville pump, accidentally discovered in 1798, which was cited and commented on in foreign works. This pump lifts a mixture of air and water. This would be the inverse case of the water pipe.[10]​.

Booster pump

The booster pump consists of a cylinder, a piston and a pipe that goes down to the water tank. Likewise, it has a valve that allows water to enter the cylinder, but not return. There is no valve in the piston, which is completely solid. From the lower end of the cylinder a second tube emerges that reaches an air chamber. The entrance to that chamber is blocked by a valve that lets water in, but not out. From the lower end of the air chamber, another pipe carries the water to a tank or hose.

Examining pump repair records and mean time between failures (MTBF) is of great importance for responsible and conscientious pump users. In view of this, the preface to the Pump User's Manual 2006 refers to statistics of "pump failures". For convenience, these failure statistics are often translated into MTBF (in this case, installed life before failure).[11]​.

In early 2005, Gordon Buck, John Crane Inc.'s chief engineer for field operations in Baton Rouge, Louisiana, examined the repair records of several refineries and chemical plants to obtain significant data on the reliability of centrifugal pumps. A total of 15 operating plants with nearly 15,000 pumps were included in the study. The smallest of these plants had about 100 pumps; several plants had more than 2,000. All facilities were In addition, they were considered "new", others "renovated", and others "established". Many of these plants - but not all - had an alliance contract with John Crane. In some cases, the alliance contract included the on-site presence of a technician or engineer from John Crane Inc. to coordinate various aspects of the program.

However, not all plants are refineries and results are different elsewhere. In chemical plants, pumps have historically been "throwaway" items, as chemical attack limits their useful life. Things have improved in recent years, but the somewhat restricted space available in the "old" DIN and ASME cable glands limits the type of closure that will fit. Unless the pump user upgrades the seal chamber, the pump only supports more compact and simpler versions. Without this improvement, the useful life in chemical facilities is usually between 50% and 60% of the refinery values.

Unscheduled maintenance is often one of the most significant costs of ownership, with mechanical seal and bearing failures among the leading causes. Consider the potential value of selecting pumps that cost more initially, but last much longer between repairs. The MTBF of an improved pump may be one to four years greater than that of its unimproved counterpart. It should be noted that the published average values ​​of avoided pump failures range between $2,600 and $12,000. This does not include lost opportunity costs. A fire occurs in a pump for every 1,000 breakdowns. Having fewer pump failures means having fewer destructive pump fires.

As already noted, a typical pump failure, based on actual reports from 2002, has an average cost of $5,000. This includes costs for material, parts, labor and overhead. Extending the MTBF of a pump from 12 to 18 months would save $1,667 per year, which could be greater than the cost of improving the reliability of the centrifugal pump.[11]​[12]​[13]​.

For the correct operation of rotodynamic pumps, they need to be filled with incompressible fluid, that is, liquid, since if they were filled with compressible fluid (any gas such as air) they would not work correctly.

Priming the pump consists of filling the suction pipe and the pump casing with liquid, to facilitate the suction of liquid, preventing air pockets from remaining inside. Since this operation is necessary in rotodynamic pumps, it is said that they do not have self-priming capacity. However, positive displacement pumps are self-priming, that is, even if they are filled with air, they are capable of filling the suction circuit with fluid.

In a circuit like the one shown in the attached diagram without any additional device, when the centrifugal pump stops, the fluid from the suction circuit falls into the tank, emptying the pump due to the vacuum created by the primary circuit.

The lifting height provided by the pump is always the same and responds to the following formula:

where is the delivery pressure, is the suction pressure, is the density of the fluid and is the acceleration of gravity.

Solving for the pressure difference we have:

From this formula it can be seen that the pressure difference achieved by the pump between the impulsion and the suction is greater the greater the density of the fluid to be moved.

So that for the specific case of water we have:

With which:

That is, if the pump is full of air, the suction pressure is 0.00129 times what the pump would achieve if it were full of water, that is, if it were primed. Therefore, if the pump is empty, the height that the water rises in the suction circuit above the water level in the tank is minimal and totally insufficient for the water to reach the pump.

On the other hand, operating a centrifugal pump under vacuum can damage the seal of the pump due to poor cooling since fluid does not circulate inside it, which helps to improve the dissipation of the heat produced by the pump.

Therefore, in pumping installations whose diagram coincides with that indicated in the attached diagram, an additional system is necessary to prevent the pump from depriming. Some of these systems are listed below:.

The pumps require hydraulic seals to prevent the fluids that are being driven from leaving the outside of the machine through the movement transmission path from the motor to the moving internals of the pump.

In the field of oil refining and petrochemicals there are mechanical pump seals standardized by API (American Petroleum Institute) which, although it is an American association, are applicable throughout the world. Each type of seal is called API PLAN. These seals can be single or double and, in addition, they may or may not have a cooling system.

There is also a pump seal classification according to ANSI.

Below is the API - ANSI equivalence of the most used sealing systems or plans:[14]​.