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TOPWhat is gear pump?
  What is gear pump?
How gear pumps work
Characteristics of gear pumps
Features of gear pumps of Daito Kogyo

Operating principle

1. The upper and lower gears (Figures A and B) rotate in the direction of the arrows.
2. The cogs engage at the center, generate negative pressure when they open and suck in liquid.
3. Liquid goes around the outside of the gears and is squeezed out when the cogs engage.
4. The opening of the outer circumference of the gears is called Top Clearance, and openings on both sides of the gears are called Side Clearance; the gears rotate in these extremely small openings.
5. The direction of the flow of liquid is from S to D in the figures.
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1. Difference from centrifugal pumps
■ Gear pumps ■ ■ Centrifugal pumps ■
Gear pumps Centrifugal pump
Compared with the centrifugal pump, the gear pump has less fluctuation of capacity as the pressure rises and has quantitative capability.
It is easy to control the capacity by changing the rotation speed.
Therefore, it is possible to control the flow rate by attaching an inverter or speed variator.
Also, since it is possible to respond to changes of viscosity of the pumped liquid and to change the rotation speed, a single pump can handle from low to high viscosities.
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2. Change of capacity due to change of viscosity
Change of capacity due to change of viscosity
When the viscosity of the pumped liquid is changed with the same gear pump, the amount that leaks from the internal openings (each clearance) to the suction side differs depending on the viscosity. The tendency is as shown in the figure above.
The higher the viscosity of the liquid, the smaller the amount of internal leakage due to rising pressure, and the smaller the difference between the flow rate determined by multiplying the capacity per rotation by the rotation speed (theoretical amount) and the actual amount.
The rate is obtained by dividing the actual capacity by the theoretical amount (volume efficiency %).
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3. Output and pump efficiency (how to read the inspection results)
Output (motor output power) PW is determined by dividing water power W by pump efficiency ηP.
 Output (motor output power) PW
Water power W represents the actual work load in transporting liquid with kW.
Water powerW
Pump efficiency changes depending on the structure of the pump, viscosity of the pumped liquid, rotation speed, etc.
See the test report as an example.


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1. Suction Capacity (Max. -9.5 m)
With its high self-priming capability, this unit is ideal for suction of fluid from an underground tank, suction from a vacuum tank, etc.
Suction Capacity (Max. -9.5 m)
2. Suction Pressure (Max. 5.0 MPa)
Even if there is back pressure on the suction side, a seal-less gear pump or a double shaft seal pump will be able to handle it.

3. Discharge Pressure (Max. 10.0 MPa)
Pumps that can withstand high pressure can be manufactured.
These feature little change of capacity for changes of discharge pressure.
Products approved for high-pressure gas can also be manufactured. Contact us for details.
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4. Sending liquid viscosity (0.3 mPa・s to 1 million mPa・s)
Any liquid can be pumped, from low viscosity to very high viscosity.
Liquid can be pumped if the relationship between the rotation speed of the pump and the piping for viscosity is appropriate.
For viscosity exceeding the above values, please consult us.

5. Capacity (Minute amount of 20 cc/min to large-capacity 5000 L/min)
A wide variety of gear pumps from small to large can be manufactured.
The capacity of a gear pump fluctuates in proportion to the rotation speed.
By leveraging the quantitative capability, it can be used as a quantitative pump.
Also, the capacity can be made variable with a speed variator, inverter drive, etc.

6. Low to high temperatures can be handled (-50 °C to +350 °C)
Thermal oil, polymer, pitch, etc. Maximum temperature: 350 °C
Brine, ammonia, engine oil, Automatic Transmission Fluid (ATF), etc. Minimum temperature: -50 °C
Various temperature situations can be handled.

7. Wide range of materials can be combined
Pump materials (FC, FCD, SC, SUS, ALBC, hastelloy, etc.)
(Acid, alkali, solvent, etc. can be handled)
For the case, cover, gear, shaft, side plate, metal, or shaft seal, various materials can be combined.
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8. Structure that can be freely combined
(1) Shaft seal
We design and manufacture various kinds of shaft seals in-house.
The most appropriate shaft seal can be selected for the pumped liquid, or specification and structure of the pump.
Seal-less Grand packing
Seal-less Gland packing
No leakage.
For petrochemicals, chemical liquids,
waste liquids, hazardous substances, etc.
Can be used for any liquid from low to high viscosity.

Single mechanically sealed Outside-type KM type Single mechanically sealed Outside-type Inside-type M type/EM type
Single mechanically sealed
Outside-type KM type
Single mechanically sealed
Inside-type M type/EM type
Used for SUS pump for chemical liquids, chemicals, liquid foods, etc. Standard type for oil in general, low viscosity oil and liquids.

Double bellows mechanically sealed Tv2 type Double mechanically sealed M2 type
Double bellows mechanically sealed
Tv2 type
Double mechanically sealed
M2 type
Vacuum-resistant suction liquid,
air hardening solution, warm liquid,
solvent, resin, varnish polymer, etc.
Vacuum-resistant suction liquid,
air hardening solution, resin, varnish polymer, etc.

Oil sealed S type (NBR, FKM) Teflon oil sealed S2 type (PTFE)
Oil sealed
S type (NBR, FKM)
Teflon oil sealed
S2 type (PTFE)
Used when leakage prevention of low viscosity, oil, or liquid is necessary. Can be used if there are problems with traditional seals when used with solvent, thermal hardening varnish, resin, etc.

Single mechanically sealed Inside type/oil seal MS type  
Single mechanically sealed
Inside type/oil seal MS type
For non-wetted outer shaft bearing
OH type oil in general - Chemical liquids,
low viscosity liquid, waste liquid, etc.

(2) Safety valve
A built-in safety valve that is built inside the pump, or an independent safety valve installed on the piping can be selected.
(3) Pump jacket
A jacket for heating/cooling can be fitted on the case, shaft seal, or whole pump.
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9. Driving method of pump
We will meet your request.
エアーモーター直結式 ギヤードモーター直結式
Air motor direct drive Geared motor direct drive
  Up to 1 million mPa・s

モーター直結式 エンジン駆動式
Motor direct drive Engine-drive
4P motor, up to approx. 250 mPa・s
6P motor, up to approx. 1000 mPa・s

変換モーター直結式 Vベルト駆動式
Speed variator direct drive V belt drive
The rotation speed can be made variable depending on the capacity. 4P motor, up to approx. 5000 mPa・s
6P motor, up to approx. 10000 mPa・s
* Consult us for specifications other than those mentioned above.
* The range of each specification may change depending on conditions. Contact us for details.

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