Pump : Centrifugal pump or basic centrifugal pump

Pump : Centrifugal pump or basic centrifugal pump

Hello friends Today we'd like to continue Pump the series. Coming to the 2 episode, we'd like to tell you about the basics of the most popular pump in the world, the centrifugal pump or centrifugal pump.

This type of pump plays a role in every application, whether it is In various industries such as petrochemicals, power plants, drilling rigs, or nuclear power plants. Or maybe it's agriculture. or in the household Because this type of pump has a cheap price. And it has a very wide usage area, including very high reliability and service life of the pump.

Centrifugal pump working principle

Centrifugal pump was invented since the year 1689 by Denis Papin. The pump relies on the working principle of "centrifugal" when the liquid flows into the suction pipe (Suction side) at position A and the fluid is sucked to the Suction eye of the Impeller at position B. Then it is thrown by centrifugal force or Centrifugal force through the Vane of the Impeller at position C,D. The fluid flows out through the discharge pipe (Discharge side) at position E.

If we classify impellers according to the direction of flow (Flow), we can divide impellers into 3. The main types are

1. Radial flow impeller Inbound and outbound are different 90 degrees.
2. Mixed flow impeller Inbound and outbound are different 45 degrees.
3. Axial flow impeller Inbound and outbound will be the same angle.

Centrifugal pump components

I would like to give an example of an Overhung Centrifugal for explaining the components. Other types of Centrifugal pumps are similar.

1. Impeller (Impeller)

Impeller or impeller of the pump Its function is to create Head and flow using the principle of centrifugal force.

The impeller can be divided into 3, the big type is

a. open impeller
b. semi-open impeller
c. Closed impeller

The use will be selected according to the Ns (Specific speed) = value as well as various characteristics of the process. Most of the materials used will be Bronze due to the light weight. and is quite corrosion resistant.

2. Pump Casing

Pump casing serves to receive fluid sent from the impeller. The casing is designed to have a rounded area. and compress the space in order to change the velocity of the fluid coming out of the impeller into pressure to send to the output side of the pump. Casing pumps have many types, such as single volute, double volute, and diffuser types.

3. Shaft Seal

Shaft seal is considered another very important part of the pump. Because the function of the shaft seal is to prevent fluid from the high pressure pump from leaking outward. If the fluid is a hazardous, flammable substance, it must have the strictest control design. We have two main types of shaft seals:

3.1 Rope Gasket (Packing Seal)

Packing seal or may be familiar with the name rope gasket It was the first generation of waterproofing. Using a rather simple principle, similar to packing rope (but actually packing rope made from a material that can withstand high heat, such as non-asbestos, asbestos, aramid, PTFE or graphite) and wrapping it around the shaft neck and then having a gland packing cover to close it.

This type of fence has the advantage of being inexpensive. and doesn't require much maintenance But the main disadvantage is The first is that there will be production loss because there must be liquid to nourish the packing and some amount will leak outside. And when used for a long time, leaks occur, it is necessary to tighten the gland packing more tightly.

Therefore, protecting the fence with packing seals is still not suitable for substances that cannot leak out, such as Substances that are hot, flammable, substances that affect health, etc.

3.2 Mechanical Seal (Mechanical Seal)

Mechanical seal is a newer type of leak protection than the first type. This type of waterproofing can withstand pressure. and the temperature can be high And most importantly, the leak is almost 0, but the maintenance cost will be more than the first type. By the principle of mechanical seal

The components have a face 2 that comes together, with a rotating face and a stationary face, using the pressure inside the pump. And the spring acts as a pressure to prevent the liquid from leaking out. The mechanical seal will have a piping plan designed to suit each use such as dirty substances, hazardous substances or water, which will have a different design. (The details I would like to share later. Because there are a lot)

The mechanical seal of the modern era is a cartridge set, which means removing and inserting, locking the nut, and it's finished. Very easy to install.

4. Bearing (Bearing)

Bearing or ball bearings Its function is to reduce friction and receive load from pump use. There are two types of bearings in pumps: radial bearings for receiving angular force and thrust bearings for receiving axial force.

5. Shaft (Shaft)

The shaft or shaft will transfer power from a drive such as a motor or possibly an engine to the impeller. The shaft of the pump must be designed to be able to receive various forces such as Torsion, Bending moment or Shear Force and must comply with Standard design, such as API pumps, the shaft will be designed to have a higher S.F. (Safety Factor) than ANSI pump, etc.

Pump Characteristic Curve

If talking about the working characteristics of a Centrifugal pump, it can be illustrated with a Pump curve.

As was introduced in the previous episode, Centrifugal pumps will work as High flow, Low head or High head, Low flow. This term is directly related to the pump curve.

Each pump will have its own Pump curve. The pump does not know how much flow and head it will use, but it will be determined by the system (System), such as valve dimming, height, and various friction values (Friction Loss).

The lines of the system will be calculated and the graph will be a System curve (red line) which will intersect with the Pump curve at this point. This is where the pump really works. We will try to design it close to Pan's BEP or Best Efficiency Point.

The Pump curve will show the main relationships. The variables are

1) Pressure (Head Pump) It is a variable that indicates how high the pump can raise the fluid. The units are m or ft. If we compare various losses in terms of elevation, the higher the pump head, the farther it can deliver.

2) flow rate (Flow ,Capacity) It indicates how much the flow rate or the amount of water that comes per unit of time is. The higher the Flow, it means The amount of water coming is greater.

3) System (System) It is a graph that indicates that this system from the starting point of delivery What kind of hydraulic loss will there be when reaching the destination? The main system curve value comes from the characteristics of the pipeline, bent pipes, valves, equipment, and various heights. The selection of a pump must be designed to be as relevant as possible to the system curve.

4) Power consumption Indicates the energy used to drive the propeller shaft or Break Horse Power (BHP). How much power is used at the point of use? If we calculate back for the motor, don't forget the efficiency loss.

5) NPSH (Net Positive Suction Head) It will tell you the minimum suction pressure. that the pump needs in order to suck things up Or as we are familiar with, why do we have to pump in water before starting the pump? There are two values for this: NPSHr or the suction pressure that the pump needs and NPSHa is the suction pressure that the system has.

Therefore, if we cut the pump curve and find that NPSHr = 1 m, it means that the pump needs the height of the water in the tank 1 m (hypothetically), we must have the height of the tank (NPSHa > 1 m or more to be sufficient).

If NPSHa is less than when, a cavitation effect will appear (causing the leaves to erode) and the liquid cannot be sucked up.

6) Efficiency Tell us about the effectiveness in use. The relationship is the ratio of the power delivered by the pump to the liquid (PH) followed by power sent to the shaft or BHP (P2)