Excellent for pumping away slush and sprinkling water to melt snow ... YOKOTA's snow-fighting pumps (PAT.)


"The train came out of the long tunnel into the snow country..." So begins the famous novel, Snow Country, by Yasunari Kawabata. While the image of a "snow country" where so much snow falls that not a spot of ground is visible is certainly romantic, to those who live there nothing is as troublesome as the snow.
By the way, did you know that if we consider the complete surface area of Japan, half the country can be considered "snow country"?

While there are various protective measures against snow and ice that are taken to protect the lives and livelihood of those living in "snow country", the greatest number of problems related to snow come from snowfall on railroad tracks and roadways.
One protective measure against snow and ice for railroads and roadways is the "slush removal system" that hydraulically transfers collected snow that has been removed from the railroad tracks or roadways and deposits it in a river. Also, there is the "sprinkler snow melting system" that melts snow by sprinkling water on the road surface.

A large number of pumps are used for these systems. While a normal pump might be sufficient in many cases, under severe conditions that require powerful suction force, such as hydraulically transferring slush with air mixed into it, an ordinary pump would not be able to perform the task.
However, YOKOTA's Self-Priming Centrifugal and Enhanced Self-Priming Pumps can be used for pumping at locations with such severe conditions. Thanks to our unique continuous air-bleeding method (PAT.), difficult pumping situations can be handled with ease.

We will use some actual examples of railroad tracks and roadways to show how the YOKOTA Self-Priming Centrifugal and Enhanced Self-Priming Pumps are utilized.

Example application 1 - "Railway station snow removal system"

Railway station F in the Hokuriku region of Japan is located in a ravine, 8.5m below the bottom of a nearby river. Due to this, natural water drainage cannot occur. This is the main reason why the snow-flowing gutters (side-gutters where removed snow flows away) constructed early-on at a large number of stations could not be used here.
In autumn of 1983, a new "slush-mixture pumping system" for snow removal was installed for the first time in all of Japan.
The system enables snow to be cleared from the tracks by just six people, thereby eliminating the tremendous delays and cancellations of trains due to heavy snowfall. To give an idea of what an advancement this represented, before the implementation of the new system, it would take 50 people using shovels one whole day to clear only the tracks around the switches.

What is the slush-mixture pumping system?

The "slush-mixture pumping system" was developed at the Snow Damage Testing and Research Center of the Niigata Prefecture Science and Technology Agency, and is a system that dumps snow into water, mixes the two into a sherbet-like consistency and then pumps it away through a system of pipes to deposit it at a far away location. It is also known as "hydropower snow transport".

Slush-mixture pumping system outline

At this station, three separate snow-flowing gutters with a total length of 1.2km were newly installed along the tracks within the station.
Since only 5.2 tons of water per minute can be pumped from the river (due to river management conditions), a water storage tank was incorporated into the snow-flowing gutters and water previously suctioned from the river is held in this tank. By combining the 10 tons of water supplied from the water tank with 5.2 tons from the river, 15.2 tons per minute can be supplied to any one of the three snow-flowing gutters.
Snow on the tracks is suctioned up by a rotary snow removal train and deposited in the snow-flowing gutters. This snow is guided to the rotating screw in the slush mixing unit where it is finely ground.
It is then passed through a grated filter and the sherbet-like slush is pumped away through steel piping along the tracks to a discharge outlet located on a river approximately 900m away. 5.2 tons of water and 1.05 tons of snow come gushing out of the discharge outlet every minute. The remaining water that passes through the filter is circulated back into the water storage tank.


Why use YOKOTA pumps?

The two main pumping jobs for this snow removal system require an "intake pump" to suction water from the river and deliver it to the system, and a "slush transport pump" to pump the slush mixture (made from the river water and the removed snow) to the discharge point on the river.

A regular pump cannot possibly offer the capabilities, as listed below, required of these pumps.

	The "intake pump" must be capable of effectively suctioning and pumping water from the river through an extended suction piping system and, moreover, through piping that goes over embankments (elevated locations).
	Since the "slush transport pump" handles the slush ground out by the mixing unit that contains 30% to 40% air, pumping capacity of a regular pump that tried to suction this slush would be drastically reduced, resulting in pump stoppage. A pump that is capable of continuous slush suction operation while discharging contained air is required.

Therefore, YOKOTA Self-Priming Centrifugal and Enhanced Self-Priming Pumps have been selected since they possess the capabilities required to satisfy these strenuous requirements.
Furthermore, YOKOTA's Non-Water Hammer Check Valve has been adopted for these pumps to prevent water hammer when the pump is stopped and ensure stable pumping.

Station grounds diagram
	1: Intake pump 2, 3, 4: Snow-flowing gutters 5: Slush mixing unit, Slush transport pump 6: Slush transport piping

River water intake	Intake pump: UHNS type with Non-Water Hammer Check Valve	Snow-flowing gutter
Slush mixing unit	Snow-flowing gutter	Rotary snow removal train depositing snow from the tracks into the snow-flowing gutter
Slush transport pump: UPS type with Non-Water Hammer Check Valve	Slush transport piping	Discharge outlet provided at river

YOKOTA Self-Priming Centrifugal Pump UHNS type (PAT.) used for water intake ... Self-priming even with extended lengths of suction piping

The YOKOTA Self-Priming Centrifugal Pump UHNS type was chosen for the intake pump because it can handle the rigorous suction requirements of extended lengths of suction piping that goes up and over embankments.
The Self-Priming Centrifugal Pump with a strong self-priming capability is used as the main pump and is supplemented by a vacuum pump to further increase self-priming capability and reduce self-priming time. Also, a water-air separating impeller is installed between the main and vacuum pumps to provide our patented "continuous air-bleeding mechanism" that prevents water or mud from entering the vacuum pump.

Since the main pump possesses its own self-priming capability, the vacuum pump can be stopped under normal conditions.

Continuous air-bleeding mechanism (PAT.)	Self-priming mechanism (PAT.)
UHNS type structural view

YOKOTA Enhanced Self-Priming Pump UPS type (PAT.) used for slush transport ... Discharges air while pumping

The YOKOTA Enhanced Self-Priming Pump UPS type with a non-clogging impeller was selected for the slush transport pump that is the central heart of this snow removal system.

The sherbet-like slush ground out by the mixing unit contains 30% to 40% air, and is in a state of "multiphase flow", i.e., air-solid-liquid mixture.
A regular pump that tried to suction this slush would suffer a loss of pumping capacity or pump stoppage. However, the YOKOTA Enhanced Self-Priming Pump has a vacuum pump that operates constantly, removing air from the mixture to ensure constant and stable pumping. Also, slush cannot enter the vacuum pump due to the operation of the water-air separating impeller.

1: Suction inlet 2: Main impeller 3: Water-air separating impeller 4: Return passage 5: Vacuum pump

YOKOTA Enhanced Self-Priming Pump mechanism (PAT.)

1.	The water-air separating impeller (3) is installed between the centrifugal pump and the vacuum pump.
2.	When operation is started, the main impeller (2) of the centrifugal pump runs idle and the vacuum pump (5) operates, eliminating the air in the suction pipe.
3.	When the air is completely eliminated, the pumping liquid flows into the pump casing, and is discharged by the main impeller (2).
4.	The mixture of water and air in the center is drawn by the vacuum pump (5), goes to the water-air separating impeller (3) from behind the main impeller.
5.	The water-air separating impeller (3) separates the water from the air instantly by centrifugal force.
6.	The water returns to the suction inlet (1) through the return passage (4), and only the air collected in the center of the water-air separating impeller (3) is drawn out by the vacuum pump (5).

Accordingly, incoming air does not block the pump suction inlet or main impeller since the suction side is always operated under the vacuum pump's maximum vacuum and bleed amount conditions. This results in stable, high-level pump performance.
Moreover, because the movement of the water-air separating impeller prevents penetration of mud, sand, and earth in the vacuum pump, pumping efficiency is ensured and safe.

Example application 2 - "Roadway sprinkler snow melting system"

The "sprinkler snow melting system" is simply a method to melt snow by sprinkling water on the roadway. As shown in the figure above, it consists of a pump that intakes water and supplies it to the sprinklers where the water is sprinkled onto the road surface via the nozzles.
While various types of water, such as ground, river, sea, or hot springs water, can be used, conventional systems mainly used groundwater. But since suctioning out too much groundwater can result in a lower water level or ground sinkage, the use of river water has recently been gaining prominence as a way to avoid these problems.

The main economic activities of Town K in Shiga Prefecture are agriculture and forestry-related. It snows 33 days out of the year and yearly snowfall is 290mm.
A sprinkler snow melting system was first introduced in this town in 1977. From that time until 1991, the system grew to consist of intake pumps in 15 locations and a snow melting pipe network with a total length of 9km. Of these 15 locations, the YOKOTA Totally Waterproof Self-Priming Centrifugal Pump System is installed in 3 locations for river water intake.

The main economic activity of Town K in Tottori Prefecture consists of pear trees, grape orchards, and other fruit farming. It snows 50 days out of the year and yearly snowfall is 900mm.
A sprinkler snow melting system was first introduced in this town in 1981. From that time until 1991, the system grew to consist of 11 sprinkling locations and a snow melting pipe network with a total length of 7.4km. The YOKOTA Totally Waterproof Self-Priming Centrifugal Pump System is also installed here in one of the locations for river water intake.
While these pumps intake river water, there are nearby river water irrigation channels for agricultural use that are not used during the winter from which water is drawn. However, since the water level is reduced in the winter, a cylindrical-shaped rubber balloon ("rubber dam") is used to block and store water, as shown in the figure, which can then be pumped out. Then, in spring, when the water is needed for agricultural purposes, the dam is deflated so that the water can be utilized accordingly.



Why use YOKOTA pumps?

While submersible or horizontal centrifugal pumps are normally used for groundwater or river water intake, they have the following disadvantages:

Submersible pumps...

	The life of a submersible pump is reduced since it is constantly submerged in water and, at worst, may start to malfunction within one year and have to be replaced.
	Even if the pump only requires maintenance, a great deal of work is needed to pull it out of the water, increasing the overall cost.

Horizontal centrifugal pumps...

	While the life of a horizontal centrifugal pump is much longer than that of a submersible one and maintenance of the pump is easier since it is land-based, it requires a site for the pump room.
	Counter-measures must be taken against noise and to prevent freezing in the winter.
	If air is suctioned into the pump, pumping capacity may be lost completely and, therefore, reliable automatic pump operation cannot be guaranteed.

However, all of these problems can be easily resolved by using the YOKOTA Totally Waterproof Self-Priming Centrifugal Pump System.


YOKOTA Totally Waterproof Self-Priming Centrifugal Pump System (PAT.) used for water intake ... Self-priming system operates easily, even underwater

Advantages of the YOKOTA Totally Waterproof Self-Priming Centrifugal Pump System

	There is no need to worry about a pump site since the pump is located in an underground pit under the sidewalk or similar location.
	The pump has an advantage in that there is no need for countermeasures against winter freezing since the temperature in the underground pit is warmer than that at ground level. Another advantage is that noise is also not a problem due to the underground pump location.
	Although water may fill the underground pit, submerging the pump, there is no reason for concern since the pump with attached submersible motor is completely waterproof.
	The greatest advantage of this pump is that it can continue pump operation easily even if air is suctioned into the system. The Self-Priming Centrifugal Pump UHPR type with submersible motor, with it's strong self-priming capability, is used as the main pump and is supplemented by the YOKOTA Vacuum Pump to further increase self-priming capability. Due to YOKOTA's unique continuous air-bleeding method (PAT.) the vacuum pump operates to bleed out air even if a large amount of air is suctioned into the system, so there is absolutely no need to worry about pump seizure due to racing of the motor.
	The YOKOTA Non-Water Hammer Check Valve (PAT.) is included to further increase operational reliability. Since the snow melting pipe is anywhere from a few hundred meters to over one kilometer in length, even one incident of water hammer is certain to spread system-wide and cause serious damage. However, the use of the Non-Water Hammer Check Valve provides reliable protection against the occurrence of water hammer.

In other words, the YOKOTA Totally Waterproof Self-Priming Centrifugal Pump System can be situated underground for hands-free operation due to it being submersible (completely waterproof) and capable of handling air mixed into pumped liquid (complete air-bleeding type). This pump system has been adopted based on this reputation for convenience.

Ground area above underground pit Self-Priming Centrifugal Pump with submersible motor in underground pit Vacuum pump in underground pit 1: Self-Priming Centrifugal Pump UHPR type (Main pump) 2: Vacuum pump 3: Non-Water Hammer Check Valve 4: No-Feed Detector 5: Main impeller 6: Vacuum pump impeller 7: Water-air separating impeller

With the addition of the Non-Water Hammer Check Valve and No-Feed Detector to the interlocked Self-Priming Centrifugal Pump UHPR type (main pump) and vacuum pump with submersible motors, the system offers completely automatic operation.

(1)	When the switch is turned on, the main and vacuum pumps are activated at the same time.
(2)	Air in the suction piping enters the main pump and then is rapidly discharged by the vacuum pump. When water fills the inside of the main pump, pumping begins.
(3)	When pumping begins, the vacuum pump automatically stops to conserve energy.
(4)	Pumping continues even if air is suctioned into the system due to the self-priming capability of the main pump.
(5)	If, by chance, a large amount of air is suctioned causing pumping capability to be lost, this will be detected by the No-Feed Detector, the vacuum pump will be activated, and air will be rapidly discharged due to simultaneous operation.

When the main and vacuum pumps are operated simultaneously, pumped water tends to flow toward the vacuum pump. With regular vacuum pumps, mud mixed in with the pumping liquid may cause a malfunction, but the air-bleeding system (PAT.) of the YOKOTA Vacuum Pump includes a water-air separating impeller (7), installed in front of the vacuum pump impeller (6), that separates water, mud, and other substances, returning them to the suction side so that only air is discharged to the outside.
The vacuum pump, protected by this structure, is able to rapidly discharge even large amounts of air so that the main pump is not stopped and continuous pumping operation is possible.

This allows completely hands-off operation capability and is a major advantage of the YOKOTA Vacuum Pump.


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

All of the above-mentioned pumps are equipped with YOKOTA Non-Water Hammer Check Valves for safe pumping.

	The Non-Water Hammer Check Valves close at exactly the moment when change in flow from normal to reverse direction occurs, that is, when the liquid in the pipes stops flowing after the pump is stopped. Due to this, water hammer due to reversed flow does not occur, thereby preventing pipe ruptures and pump damage.
	The single-disk, simple construction eliminates breakdowns. Maintenance costs can be reduced considerably.
	The No-Feed Detector can also be installed optionally.

Pressure change with time after pump operation is stopped
YOKOTA Non-Water Hammer Check Valve	Conventional check valve

For details of each product, please refer to
Self-Priming Centrifugal Pump UHN series (UHNS, UHPR types)
Enhanced Self-Priming Pump UPM, UPS types
Non-Water Hammer Check Valve SL series