• Gear pumps are positive displacement pumps and are of rotary type
• with the difference that their design and construction are simpler and their output flow is uniform
• And it does not need a one-way valve on the suction side.
• The gear pump is made in different sizes and types of gears.
• The number of teeth on the gear can be from two to more.
• Gear pumps are mostly used for lubrication.

External gear pump

• The external gear water pump is a type of positive displacement water pump that is usually used to move and measure liquids.
• The reason for the name of this water pump is that this pump has two side-by-side or external gears
• And this feature it distinguishes from the internal gear water pump. The internal gear water pump has one gear
• which is placed in another gear.

Danfoss Gear Pumps External-Gear-Pump-Principles

The external gear pump is a functional device with high tolerance

• and is able to work against high differential pressures.
• How the gear water pump works is shown in diagram 1.
• A drive gear driven by a motor turns another gear in the opposite direction.
• When the gears rotate, the fluid in the gear teeth moves between the housing and the outer space of the gear
• and it is transferred from the inlet part of the pump to the outlet part.
• It is worth noting that the pumped fluid around the ribs, not between them. moves

Gear rotation

• Until the delivery of a volume of liquid sucked (input part) to discharge (output part) it continues almost without any fluctuation.
• The rubbing of the ribs together causes the liquid to be pushed out of the pump and the pumping discharge.
• Another important advantage of the external gear water pump is its self- driving capability.
• A gear water pump is able to be self-priming because the gears send air into the suction line.
• This creates a slight vacuum that allows the atmospheric pressure to pressurize the liquid and send it to the water pump inlet.
• This feature of gear water pump, when there is a need to place the water pump above the liquid level
• And the liquid should be lifted to the water pump, it is a very good option.
• Since the gear water pump cannot create a complete vacuum, the total lift should not be more than half of the atmospheric pressure .

What is a gear pump?

A gear pump, also known as a thickener pump, is a positive displacement type pump that encloses a fixed volume of fluid and then transfers it using gears. During pumping, this pump provides a uniform and smooth flow according to the rotation speed of its gears.

Gear pumps use the rotating action of gears to transfer fluids. The ribs create suction at the inlet of the pump, as a result of which the fluid is drawn into the pump and placed inside the cavities of the pump ribs, and finally transferred to the outlet pipe and liquid discharge.

Types of gear pumps

In general, there are two types of this pump: external gear pump and internal gear pump .

 

External gear pump

The external gear pump (External Gear Pump) consists of two integrated and connected gears, each of which is supported by an independent and separate shaft. Generally, one of the gears is driven by the motor (drive) and then this gear turns the other gear (drive). However, in some cases, both shafts may be driven by independent motors. The shafts are supported using bearings on each side of the casing.

How these pumps work

This is how the ribs on the outside of the pump, that is, on the inlet side of the pump, suck the fluid into the pump and introduce a large volume of liquid into the cavities. At this time, the liquid is trapped by the teeth of the gears , while the gears continue to rotate, unlike the casing. The entrapped liquid is transferred from the inlet to the discharge tube around the pump casing. As the teeth of the gears are placed on the discharge side of the pump, the fluid volume is reduced and the fluid is pressurized.

 

Due to the complete connection of the ribs to each other, no liquid is transferred from the inside of the circuit between the ribs. The close relationship between the ribs and the casing allows the pump to perform suction on the inlet side of the pump and prevent liquid leakage on the outlet and discharge side of the pump; Although the possibility of leakage is only in the case of liquids that have a low viscosity.

The design of gears in external gear pumps is one of three simple and smooth, helical or chevron designs .

Internal gear pump

The internal gear pump, which is also known as the moon and star pump due to the shape of the gears , has the same function as the external gear pump; This pump has two gears connected to each other and of different sizes, one of which rotates inside the other. The larger gear (rotor) is an internal gear in the sense that its teeth are inside. Inside this internal gear, a smaller external type gear (the teeth are on the outside) is placed.

The smaller gear is designed to be attached to the rotor so that the teeth of the gears mesh at one point. The piston and bushing connected to the pump puts the chamber in position. A crescent-shaped fixed piece or spacer fills the empty space created due to the out-of-center position of the internal gear and acts as a seal between the input and output paths.

The internal gear pump can only be a simple gear in terms of gear design.

The following table is a general comparison between internal and external gear pumps:

External gear pump	Internal gear pump
Two identical gears are placed together and the drive gear is connected to the motor and rotates the other gear.	An external gear wheel is placed inside another gear with an internal gear (drive) and is moved by it.
It works with high pressure.	It works with medium pressure.
Compact structure and cheaper design	Larger structure and more expensive design
It is suitable for medium and low temperature fluids.	Can be used for high temperature fluids.
Larger output sizes and higher capacities	Smaller output sizes and higher capacities
Ability to pump in two directions if using a simple gear	It can always work both ways.

Application and advantages of gear pump

Gear pumps have a limited number of moving parts and are very compact and simple. Comparatively, these pumps are not able to pump fluids with the pressure produced by reciprocating pumps or centrifugal pumps, but they have higher pressure and efficiency than vane pumps or earring pumps. Gear pumps are especially suitable for pumping oil (gear pump oil) and other liquids with high viscosity.

External gear pumps are able to maintain higher pressure and flow due to the support of a stiffer shaft and greater tolerance. Internal gear pumps have better suction and are suitable for high viscosity liquids. However, these pumps have a useful operating range for viscosities from 1 to over 1 million centipoise.

Since the output is directly related to the rotation speed, gear pumps are usually used for metering and mixing operations. Gear pumps can be designed to pump aggressive liquids. Although these pumps are usually made of iron or stainless steel, there are also new alloys and composites that allow these pumps to pump corrosive liquids such as sulfuric acid, sodium hypochlorite, iron chloride, and sodium hydroxide.

In addition, external gear pumps can be used in hydraulic applications, which are typically required in vehicles, lifting machines and factory equipment.

Reverse rotation of a gear pump creates a hydraulic motor (hydraulic gear pump) using oil pumped from other parts in a system. This ability to provide power in cases where the use of electrical equipment requires space, is expensive or impossible; It is very useful. For example, tractors and lathes are equipped with external gear pumps with a drive motor, to provide the power required for their services.

The table below lists some of the most common applications of our type of pumps:

Gear pump type	Foreign	Internal
Various fuel and lubrication oils	✔	✔
Chemical and polymer additives	✔
Mixing chemicals	✔
Industrial and agricultural hydraulic applications	✔
Acids and oxides (with ) stainless steel or composite body	✔
Resins and polymers		✔
Alcohols and solvents	✔	✔
Asphalt and bitumen		✔
Polyurethane foam (isocyanate and polyol)		✔
Food: corn syrup, peanut butter, cocoa butter, chocolate, vegetable fats, vegetable oils, animal feed		✔
Color, ink and pigment		✔
Soap and surfactants		✔
Glycol		✔

Limitations and disadvantages

Gears should be regularly lubricated and should not be left dry for long periods of time. The tight and close relationship between the fins and casings means that these types of pumps are particularly sensitive when working with abrasive fluids or fluids containing adsorbed solid particles.

However, some gear pump designs, especially internal types, also allow solids handling. External gear pumps have 4 bearings inside the pump housing, so they are less suitable for dealing with abrasive fluids. Internal gear pumps are stronger in this respect because they only have 1 bearing (sometimes 2).

Buy a gear pump

In general, if the pumped liquid is expected to contain solid and abrasive particles, it is better to choose and purchase a pump with a higher capacity so that it can be used at lower speeds to reduce wear. It should be kept in mind that the volume flow rate of a gear pump decreases at low speeds. A gear pump should not be used beyond its recommended speed.

For high temperature uses and applications, ensuring that the operating temperature is compatible with the pump specification; It is very important. The increase in the temperature of the casing and ribs reduces the distance in a pump and can also increase wear and in more severe cases, even pump failure.

Even in spite of observing the best safety and precautionary measures, gears and bearings of gear pumps generally wear during rotation. Leakage of the pumped liquid from the discharge outlet side to the suction inlet side. It also reduces the efficiency of the pump.

Internal gear pumps that operate at low speeds are usually preferred for shear-sensitive liquids such as food, paint, and soap. On the other hand, external gear pumps are not suitable for these applications due to higher speeds and less variety of design. Internal gear pumps are also preferred when hygiene is important.

Gear pump in another view

• The drive shaft gear pump is connected to the drive gear of the hydraulic pump with a pin.
• The idler gear is engaged with the driving gear and both rotate together.
• The teeth of the engaged gears together seal the inlet and outlet valves of the gear pump relative to each other.
• With the rotation of the gears, the teeth of the two gears are opened in the input part of the gear pump.
• The opening of the teeth is like a suction and volume expansion in this part
• And it causes the fluid to be pushed into the pump due to the air pressure in the tank.
• This fluid is then directed to the pump outlet valve in the empty space between the gear teeth and the gear pump body.
• In this part, the teeth of two gears are close together
• and causes the fluid to be pushed out.
• The seal between the teeth does not allow oil
• which passes through the middle of the gear pump and returns to the inlet.

There are two types of gear pumps:

• Foreign
• Internal

In this section, various types of gear pumps from reputable brands are introduced.

• Hydraulic pumps can be supplied in different types. One of these types of pumps is a gear pump.
• which are in two types of internal gear pump and external gear pump.
• Gear pumps are positive displacement pumps.
• These pumps have a shell inside which the ribs are placed close to each other
• And this type of placement causes movement and transfer of fluid.
• The main movement of these pumps is rotary.
• In these pumps, a limited volume of fluid is moved per revolution.
• Gear pumps have two gears that are engaged in each other
• And finally, they cause fluid pumping. Among these two gears, one of them is the driver and causes the rotation of the other.
• The physical contact between the gears causes a part of the fluid to move between the inlet and outlet ports, and the space inside the pump housing is completely sealed.

There are different types of gear pumps, including:

1. Internal gear pumps (Internal Gear Pump)
2. External gear pumps (External Gear Pump)
3. Lobe pumps
4. Screw pumps
5. Gyrotor pumps (Geroto

Rexroth internal gear pump

Internal hydraulic gear pump can be supplied in different brands. Rexroth internal gear pump models include PGF, PGH-2X, PGH-3X, PGP
Roxan Parsian Company currently has the ability to provide these models of Rexroth gear pumps.

Inside the gear pump, two gears move opposite to each other, the first one is connected to the motor shaft and the second one is a round gear. The fluid enters the pump from the inlet chamber and passes through the teeth of the gears and the wall of the pump chamber. Due to very small distances, the fluid cannot pass through the center of the pump.

For this reason, the two flows are combined again and pushed to the pump outlet.
Gear pumps can operate in both directions and this is a significant feature in some systems. Because the bearings of this gear pump are under load in only one direction (output pump pressure), they are called unbalanced pumps. For this reason, these pumps tend to wear disproportionately and only from one side.

In the internal gear pump, an external drive gear is placed inside an internal ring gear. When the gears start to rotate, the teeth are separated and suction occurs, then the fluid enters the pump. The gears are sealed in the form of crescent-shaped walls. The internal gear pump can be called the least efficient type of hydraulic pumps, but due to its greater laxity than other types of pumps, they have a good tolerance against hydraulic fluid contamination. The maximum working pressure of this gear pump is 140 to 200 bar and their volume cannot be adjusted.

One of the reasons for the superiority of the gear pump is the very suitable suction of the gear pump at a constant speed. Pollution has very little effect on the operation of the gear pump. The fact that the gear pump does not require special conditions and places for installation. The simple and strong mechanism of the gear pump Oh and… he pointed out.

Danfoss Gear Pumps Bucher Hydraulics Gear Pumps External-Gear-Pump-Principles