Self-Priming Centrifugal Pump

Self-Priming Centrifugal Pump
UHN series

Outstanding self-priming performance even under extreme conditions

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Self-Priming Centrifugal Pump

Patented in Japan, U.S.A., other



Total head




Standard centrifugal pumps have no self-priming capability and are incapable of pumping when water flow is discontinued in the suction pipe. The oval shaped self-priming pump has weak self-priming force at locations where back pressure is present, and the higher the pump head, the harder to self-prime the water.
The YOKOTA Self-Priming Centrifugal Pump has the same pumping capability for high head pumping as other centrifugal pumps, however its self-priming force is extremely strong at 60-90kPa (6-9m water column), which enables the pump to be used even under extreme conditions.

For suction pumping with outstanding self-priming power:

UHN type

For intake piping across embankments or long intake pipes:

Priming strengthened UHNS/UHNK types

For high density slurry:

Slurry resistant UHT type

For installation in places subject to submersion:

UHPR type with submersible motor

For self-priming sanitary specifications:

SUH type

Features of the YOKOTA Self-Priming Centrifugal Pump

Outstanding self-priming power

The internationally patented water-air separating mechanism reaches a maximum vacuum of 60-90kPa (6-9m water column) and displays outstanding self-priming power.

No problem with suction of air during pumping

A large amount of incoming air can be separated and discharged during pumping. Even if pumping becomes subject to suction or mixture of air due to fluctuations of suction conditions, it continues pumping, constantly discharging air, and restores normal pumping operation as soon as suction conditions return to normal. Even continuous suction of air-containing water (i.e., gas-liquid two-phase pumping) is possible.


Even if cavitation develops due to fluctuations of suction conditions such as water level, temperature, or vacuum level on the suction side, this pump can still continue its pumping operation. Therefore, this pump does not require allowance for NPSH, and enables stable pumping operation even under fluctuating suction conditions. It naturally shows outstanding performance for extraction from sealed (vacuum) tanks.

Simple structure without any inlet valve, No need for a foot valve

Due to its simple structure without any inlet check valve, it is robust and easy to maintain. Moreover, there is no need for installing a foot valve or an intermediate valve on the intake side under ordinary operating conditions.
Operation is also easy with no need for priming.

Intake piping across embankments or long intake piping is possible

Because of superior intake power, intake pipes can be installed across embankments.
Intake piping with long piping is also possible.

Outstanding pumping performance

This single-suction, single-stage centrifugal pump displays outstanding pumping performance in a wide range of specifications.

Large selection of models, Large selection of materials

This self-priming pump has an incomparably wide variety of models available for easy selection. Further, a wide variety of materials are available, including FC, SCS and YOKOTA's corrosion and wear resistant special stainless steel casting (YST), to meet the needs of various kinds of liquid.

Construction that can meet a wide range of specifications

Standard constructions include semi-open impellers for small pumps and closed impellers for medium and larger pumps.

The impeller has been improved to form ideal blades for high efficiency.

An oil bath lubrication system is adopted for bearings.

Maintenance is easy to perform because construction is simple and the number of parts in the water passage section is minimized.

Stable quality

All special material products are manufactured internally in a continuous process to ensure stable quality.

Principle of self-priming (PAT.)

The pump casing consists of a smaller passage and a larger passage forming a semi-double volute and a cavity holder in the discharge nozzle.


Flow of circulation

During self-priming, the water discharged from passage A in the semi-double volute returns to the impeller through passage B-C, and is discharged again into passage A.


Removal of bubbles

This recirculation flow mixes the water and the air in the center with intense vortex D within the impeller and discharges it into passage A.


Water-air separation and exhaust

The water-air mixture is led from passage A to discharge nozzle B in a cyclonic state and automatically separated by centrifugal force, and then the water is recirculated through passage B-C. The separated air is then held by cavity holder E, and compressed and discharged.

Self-Priming Centrifugal Pump UHN series

Self-Priming Centrifugal Pump / Principle of self-priming  (PAT.)


The YOKOTA Self-Priming Centrifugal Pumps can be used even under extreme conditions. They can be used, for example, as chemical pumps for liquids containing air, pumps for mixing air bubbles in an aeration system (i.e., gas-liquid two-phase flow pumps), condensate pumps, drain pumps, and pumps for extraction from sealed tanks.

Chemical industry:

Acids, Alkaline liquids, Solvents, Slurry liquids, other

Food industry:

Brewery, Sugar refining, other

Mining industry:

Seawater, Slurry liquids, other

Paper industry:

Pulp, Effluent, White water, Black water, other

Electric power:

Exhaust gas desulfurizer (Limestone slurry pumps, other), Seawater, Water treatment, other

Electronic industry:

Ultra-pure water manufacturing devices, Acidic waste water, Polishing waste water treatment, other

Aquarium, Fish farming:

Seawater suction, Circulation pumps, other


Hot springs, Hot oil, other

Self-Priming Centrifugal Pump UHN type
Self-Priming Centrifugal Pump UHN type
Self-Priming Centrifugal Pump UHN type

Example applications and installations (Special cases where difficult pumping conditions are present)

For aquariums ... UHN type
Made of extraordinary seawater resistant YST alloy

More details >

"Current Topics: Aquarium"

Self-Priming Centrifugal Pump UHN, Used in many aquariums, YOKOTA Seawater Pumps made of YST Alloy

For irrigation pumping stations ... UHN type
Automatic water supply with extremely small tank

More details >

"Current Topics: Irrigation Supply"

Self-Priming Centrifugal Pump UHN, Small tank, but no severe, intermittent operation, YOKOTA Mini-Tank Automatic Water Supply Equipment

For water intake ... Priming strengthened UHNS type
Suction of water through long piping over embankments

More details >

"Current Topics: Snow Removal"

Self-Priming Centrifugal Pump UHN, Excellent for pumping away slush and sprinkling water to melt snow, YOKOTA's snow-fighting pumps

For fish farms ... Priming strengthened UHNK type
Suction of seawater from the sea at a distance of 400m

More details >

"Current Topics: Seawater Intake"

Self-Priming Centrifugal Pump UHN, Resolving the concerns of seawater pumping, YOKOTA Seawater Intake Pump

For power plants ... Slurry resistant UHT type
Resolving problematic self-priming of slurry liquids

More details >

"Current Topics: Slurry Self-Priming"

Self-Priming Centrifugal Pump UHN UHT, Resolving problematic self-priming of slurry liquids at power plants, YOKOTA Slurry/Corrosion Resistant Self-Priming Centrifugal Pump

For undersea tunnels ... Submersible UHPR type
Pumping ensured even if submerged in seawater

More details >

"Current Topics: Undersea Tunnel"

Self-Priming Centrifugal Pump UHN UHPR, Used in draining operation at Kanmon and Seikan Tunnels, YOKOTA pumps and valves

This is a self-priming type pump for suction pumping.
For the non-self-priming type (for force pumping) with similar specifications, please refer to
Centrifugal Pump UEN series.

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