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Resolving the concerns of seawater pumping ... YOKOTA Seawater Intake Pump (PAT.)

The Yokota Seawater Intake Pump provides suction of seawater from the sea at a distance of 400 meters.
The Yokota Seawater Intake Pump provides suction of seawater from the sea at a distance of 400 meters.

The ultimate method of solving water shortages in various countries is the use of the inexhaustible supply of seawater.
In this respect, there is a growing trend for the use of seawater. Salt production is one obvious use, however, recently factories and power generating facilities are using vast amounts of seawater for cooling and, with the use of desalination equipment, major production of drinking water is being carried out. Moreover, fish farms are increasingly finding it easier to raise fish in land-based hatchery ponds by pumping in seawater rather than managing a fish farm on the sea itself.


What are the problems with seawater intake?

In the past, seawater intake was generally done using immersion type pumps such as a submerged pump or vertical pump.
The main reason for this was because of the poor seawater pumping efficiency of land-based pumps.
Difficult pumping conditions are common due to factors such as poor self-priming efficiency from the extrication of air and bubbles which occurs easily in seawater, too much distance from the water suction intake, and pipes crossing over embankments. With no strong self-priming pumps that could meet these demands, the solution closest at hand was "forced pumping operation" with submergible pumps.

However, for submerged pumps, because the pump motor is submerged together with the pump, there are concerns with the power supply, corrosion, and the danger of damage caused by rough seas. Added to this is the troublesome work of pulling up a submerged pump to perform maintenance inspection.

As for vertical pumps, because the main part of a vertical pump is submerged in water, they are prone to the danger of flood-tides and typhoons. What's more, the large size of the equipment means higher construction costs, and the added trouble of performing inspection on the main part of the pump.

Although there are land-based volute pumps equipped with a vacuum pump for priming liquid, it is usually the case that the vacuum pump is cut-off at the same time priming is finished to prevent damage to the vacuum pump from penetration of seawater. For this reason, if air suction occurs during pump operation, pumping becomes difficult.
Also, because suction power is not strong enough, pumping through suction pipes across embankments is not possible.
This situation is further problematic in areas where boring through embankments or barriers is not permitted by port and harbor regulations. Consequently, it becomes necessary to set a pump on a landfill at the same height as the embankment. This only increases the concern over loss of pumping ability due to the increase in suction height.

The newly conceived YOKOTA Seawater Intake Pumps are the clear answer to these concerns.


What is different about YOKOTA Seawater Intake Pumps?

Seawater intake pump comparative chart

Submerged pump

Vertical pump

Conventional centrifugal pumps equipped with a vacuum pump

YOKOTA Seawater Intake Pumps (Patented continuous air-bleeding type)

Submerged pump
Vertical pump
Conventional centrifugal pumps equipped with a vacuum pump
YOKOTA Seawater Intake Pumps

Danger of damage from flood-tides and typhoons.
Maintenance inspection extremely difficult.
High concern for power supply.

Danger of damage from flood tides and typhoons.
Maintenance inspection is difficult.
High construction cost due to large facility requirement.

Pumping problems due to air suction.
Uncertainty of pumping efficiency with increase of pump head.
High construction cost due to pump set-up on landfill.

Air suction during pumping is no problem.
No loss of pumping efficiency.
Low construction cost because piping across embankments is possible.


YOKOTA Seawater Intake Pumps, with their patented construction of a "continuous air-bleeding" method which interlocks a bleed pump (vacuum pump) to the centrifugal pump, provide strong priming efficiency without penetration of seawater or muddy water into the vacuum pump even during continuous suction.

Superior suction performance

Superior suction performance from the continuous operation of the vacuum pump.

Air intake is no problem

Using continuous air-bleeding, pumping continues without any problems, even if air is sucked into the system or air dissolved in seawater becomes extricated during pumping.

Piping across embankments is possible

Due to the superior pumping efficiency, piping shaped around embankments and various types of man-made and natural sea barriers is possible.

Complete automatic operation possible

Because the pumps require neither a single drop of priming liquid nor a cut-off operation for the vacuum pump, complete automatic operation is realized.

Simple maintenance inspections

Maintenance inspection is easy and safe for pumps set in land-based pumping houses.

Cost reduction

Construction costs are cheaper because pipe construction over embankments is possible, and large facilities or landfill preparation is unnecessary.


The YOKOTA Seawater Intake Pump has received high marks based on the above merits and is being used widely both domestically and abroad.


What is the continuous air-bleeding YOKOTA Vacuum Pump?

The greatest advantage of the continuous air-bleeding method lies in the YOKOTA's unique vacuum pump.
The patented construction of the vacuum pump with its built-in water-air separating impeller does not allow penetration of seawater or muddy water into the vacuum pump even during continuous air-bleeding.

1.

When operation begins, both the main pump and vacuum pump operate simultaneously, removing air in the suction pipes.

YOKOTA Vacuum Pump

2.

When the air is completely removed, pumping water reaches the main pump casing and is discharged by the main impeller.

3.

The water-air mixture in the center of the main impeller is drawn by the vacuum pump to the water-air separating impeller.

4.

The water-air mixture is separated instantly by centrifugal force by the rotation of the water-air separating impeller.

5.

The water follows a return passage to the main pump intake, and only air collected in the central area of the water-air separating impeller is drawn into the vacuum pump.


Accordingly, the suction intake side of the main pump is always operating under conditions of maximum vacuum and bleed amount from the vacuum pump, and as a result, pumping is not interrupted because there is no air obstruction in the main pump.

YOKOTA Vacuum Pump VP-K type (PAT.)

YOKOTA Vacuum Pump VP-K type (PAT.)

1: Suction intake

2: Water-air separating impeller

3: Separated water outlet

4: Vacuum pump impeller

5: Exhaust air outlet


The following main pumps are available in consideration of self-priming ability and pumping capacity.

Self-Priming Centrifugal Pump UHN type (small-medium capacity, self-priming type):

Suction power is enhanced with the interlocked vacuum pump.

Process Pump UB type (medium capacity, self-priming type):

Suction power is enhanced with the interlocked vacuum pump.

Double Suction Volute Pump HD type (large capacity, non-self-priming type):

Large capacity, self-priming type when interlocked with a vacuum pump.

Mixed-Flow Volute Pump YM type (large capacity, non-self-priming type):

Large capacity, self-priming type when interlocked with a vacuum pump.


The following are three example applications of the pump.


Example application 1 - "Shrimp hatchery"


YOKOTA Seawater Intake Pumps have actually been supplied to various facilities such as experimental fishery stations, fish hatcheries, and fish farms, however, the following is an example of an application at a large-scale shrimp hatchery.
Good water maintenance is the foundation of the fishing industry, and for fish farms this literally means a stable, economic supply of seawater is what is most important. Because shrimp require especially pure seawater, it is delivered to the hatchery from a distance of 350m offshore.

Shrimp hatchery

At such a distance, and in consideration of possible damage caused by weather conditions such as typhoons, the safeness and manageability of submerging a pump in the sea (submerged/vertical pumps) is unsuitable.
As a result, land-based pumps have been preferable, with the installation location set across a flat surface 50m from the shoreline and at a height of 2.5m above the sea surface. However, this type of installation requires extensive piping of over 400m.
Nonetheless, stable and assured pumping is indispensable, because as far as the shrimp hatchery is concerned, pumping problems would only result in product loss.
In answer to these concerns, we have thoroughly developed a continuous air-bleeding system and created a package with even greater self-priming power in our YOKOTA Self-Priming Centrifugal Pump UHN type interlocked with the YOKOTA Vacuum Pump VP-K type. Added to this package is an assembly including the YOKOTA Non-Water Hammer Check Valve for absolute protection against water hammer and, together with the No-Feed Detector and control panel, this system provides complete automated operation.

Water pumped approx. 400m from offshore

Suction piping

Water pumped approx. 400m from offshore
Suction piping
Inside of pump housing



Discharge to hatchery pond



Complete view of hatchery
Inside of pump housing
Discharge to hatchery pond
Complete view of hatchery


YOKOTA Automatic Seawater Pumping System, a pump package with complete functionality

YOKOTA Automatic Seawater Pumping System

1:

Main pump

2:

Vacuum pump

3:

Non-Water Hammer Check Valve and No-Feed Detector

4:

Priming detector

5:

Common base plate

6:

Main pump motor

7:

Vacuum pump motor

8:

Control panel

Main pump:

UHN type 200mm x 3.6m3/min x 18.5m x 1750rpm x 18.5kW

Vacuum pump:

VP-K type 5.5kW


This system's operation order is as follows:

1.

When the switch is turned on, the vacuum pump is activated.

2.

When the priming detector detects that the suction piping is at full capacity, the main pump is activated and pumping begins. To conserve energy, the vacuum pump is stopped.

3.

Even if air is sucked into the system or air dissolved in seawater becomes extricated during pumping operation, the self-priming mechanism in the main pump itself processes these types of air intake without any problem for stable, continuous pumping.

4.

In the unlikely event a large amount of air is sucked into the system causing pumping problems, the amount of water passing through the Non-Water Hammer Check Valve approaches zero, whereby the built-in No-Feed Detector detects this condition, activates the vacuum pump and automatically returns operation to number 1. above.

5.

If the water intake surface changes severely and a large amount of air intake is anticipated, the vacuum pump can be switched to continuous operation for stable and continuous pumping operation.


The UHN type pump itself, which is used here as the main pump, provides high performance self-priming.


Yokota Self-Priming Centrifugal Pump UHN type (PAT.) features

Casing consists of a simple construction with a semi-double volute and a cavity holder. A single-suction, single-stage pump displaying outstanding pumping efficiency in a wide assortment of specifications.

Outstanding self-priming power, with a maximum vacuum reaching 60-90kPa (6-9m water column).

Low NPSH. Even if cavitation develops due to fluctuation in intake conditions, this pump can still continue pumping operation and does not require allowance for NPSH.

Even if pumping becomes subject to air suction or mixture of air during pumping operation, it continues pumping without a problem. Even continuous suction of air-containing water (i.e., gas-liquid two-phase pumping) is possible.


Self-Priming Centrifugal Pump UHN series

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Self-priming mechanism

Self-priming mechanism (PAT.)



Example application 2 - "Chemical plant"


This example concerns a pump application at a large chemical plant.
Because a large amount of seawater is needed for cooling, the main pump that the plant uses is a large capacity YOKOTA Double Suction Volute Pump. Having adopted the continuous air-bleeding method, the convenience of a piping arrangement over higher elevations is possible without fear of air suction during pumping operation.

YOKOTA Double Suction Volute Pump

Main pump:

HD type

50m3/min x 25m x 900rpm x 300kW

Vacuum pump:

VP-K type

2.2kW


pump application at a large chemical plant



Chemical plant



Example application 3 - "Thermal power plant"


We have numerous pump applications for thermal power plants, however, the example we are discussing here concerns the "screen cleaning pump" that cleans the screen at the seawater intake of a thermal power plant.
The main pump used here is the medium capacity YOKOTA Double Suction Volute Pump. Having adopted the continuous air-bleeding method, it is a completely automatic, high-efficiency self-priming pump.
Moreover, with the aim of reducing inspection frequency by protecting the equipment from water hammer, the YOKOTA Non-Water Hammer Check Valve has been adopted for absolute protection against water hammer.
The main pump and Non-Water Hammer Check Valve have also been produced with the particular aim of reducing inspection frequency by protecting the equipment from seawater corrosion (such as crevice corrosion) using YOKOTA Seawater Resistant Stainless Steel YST130N.

YOKOTA Double Suction Volute Pump


Main pump:

HD type

7m3/min x 75m x 1800rpm x 120kW

Vacuum pump:

VP-K type

3.0kW


Water hammer protection using the Non-Water Hammer Check Valve

Corrosion protection using Seawater Resistant Stainless Steel YST130N


Thermal power plant

screen cleaning pump



Regarding the YOKOTA Non-Water Hammer Check Valve (PAT.)

The valve opens and closes in response to water flow, therefore there is no delay in valve closure and water hammer does not occur.

The single-disk, simple construction eliminates breakdowns. Maintenance costs can be reduced considerably.

The No-Feed Detector can also be installed optionally.


Pressure change over time after pump operation is stopped

YOKOTA Non-Water Hammer Check Valve
Conventional check valve
YOKOTA Non-Water Hammer Check Valve
Conventional check valve


Regarding YOKOTA Seawater Resistant Stainless Steel YST130N

YST130N is a duplex stainless steel alloy independently developed by YOKOTA with excellent corrosion resistance to seawater and chemicals.
Results of actual field tests clearly show that YST130N has excellent crevice and pitting corrosion resistance.

Crevice corrosion resistance

Loss due to crevice corrosion
Field test with actual liquid
(seawater + hypochlorous acid (90-100ppm))
Test period: approx. 1 year and 9 months
Crevice corrosion resistance

Test piece after field test
YST130N
SUS316
YST130N
SUS316

Pitting corrosion resistance

Loss due to pitting corrosion
5% ferric chloride 40 deg C, 50hr

Pitting corrosion resistance

Test piece after field test
YST130N
SUS329J1
SUS316

YST130N

SUS329J1

SUS316



For details of each product that makes up the Seawater Intake Pump System, please refer to
Self-Priming Centrifugal Pump UHN series
Process Pump UB series
Double Suction Volute Pump HD type
Mixed-Flow Volute Pump YM type
Non-Water Hammer Check Valve SL series
Seawater Resistant Stainless Steel YST130N


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