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A chemical cargo pump with 30 years of achievement ... YOKOTA Enhanced Self-Priming Pump UPS type (PAT.)

Tanker Cargo Handling

Photo provided by marine firm A


Is it possible for a centrifugal pump to effectively suction chemical liquids?

Chemical tankers that can hold large amounts of various chemical liquids have emerged as the most efficient and important means of delivering these chemicals to Japan as it is surrounded by the sea in all directions.
Along with chemical tankers, a chemical cargo pump that is used for loading and unloading chemical liquids has also been developed.

By the way, do you think that a chemical cargo pump must be a gear or screw pump to effectively suction chemical liquids?
While it is, in fact, difficult to pump chemical liquids with a normal centrifugal pump, the YOKOTA centrifugal-type Enhanced Self-Priming Pump, in use since 1973, has gained a widespread reputation as an effective chemical cargo pump.

How is the Enhanced Self-Priming Pump being utilized?

The Enhanced Self-Priming Pump-equipped chemical tanker
An Enhanced Self-Priming Pump is located in the pump compartment
The Enhanced Self-Priming Pump-equipped chemical tanker
An Enhanced Self-Priming Pump located in the pump compartment
(Main pump in the front, Vacuum pump at the rear)


Why use the Enhanced Self-Priming Pump?

We will explain how the YOKOTA Enhanced Self-Priming Pump is utilized using the examples of two tankers.

Tanker(owned by marine firm H, 492 tons)
Tanker (owned by marine firm D, 449 tons)

The tanker in the above-left photo (owned by marine firm H, 492 tons) was constructed in 1991. It is a chemical tanker that mainly transports acetic acid and is equipped with two Enhanced Self-Priming Pumps UPS type.
Pump specifications: 150mm bore diameter, 200m3 per hour discharge rate, 50m pump head capability, and interlocked with a vacuum pump VP-S type.

The figure below is a layout drawing of the pump. It should be noted that the pump compartment is located on the deck.
A gear pump can be used only from the bottom of the ship, and therefore proves troublesome when cleaning the tank or pump due to its location. With regards to safety, it is far more convenient to locate the pump on the deck of chemical tankers that handle toxic and volatile liquids. The Enhanced Self-Priming Pump can be installed on the deck with no problems whatsoever. Of course, it could also be used at the ship bottom, allowing the user to choose the best option.

Layout with the pump equipped on the deck
Layout with the pump equipped on the deck

The tanker in the above-right photo (owned by marine firm D, 449 tons) was constructed in 1992. It is a chemical tanker that mainly transports acrylic acid and is equipped with three Enhanced Self-Priming Pumps UPS type.
Pump specifications: 100mm bore diameter, 120m3 per hour discharge rate, 50m pump head capability, and interlocked with a vacuum pump VP-S type.

For this ship, the pump compartment is located on the mid-deck.
Since acrylic acid is a highly toxic liquid and other liquids are also often transported in place of acrylic acid, from an efficiency and safety standpoint, the ship's captain and crewmembers are pleased to have the pump located on the deck.


What are the advantages of using the Enhanced Self-Priming Pump?

Given the examples from above, it is clear that the YOKOTA Enhanced Self-Priming Pump is a chemical cargo pump system that can substantially improve the efficiency of loading and unloading work.

It can be installed on the deck.

It can substantially improve the efficiency of loading and unloading work.

It is safe.

Maintenance is easy and economical.



Enhanced Self-Priming Pump liquid suction structure (PAT.)

Enhanced Self-Priming Pump (PAT.) liquid suction structure

1:

Bleed pipe

2:

Float valve

3:

Suction pipe

4:

Pump suction inlet

5:

Main impeller

6:

Water-air separating impeller

7:

Return passage

8:

Non-Water Hammer Check Valve


The main pump is in the middle of the structural view, and at the above right is the vacuum pump.

1.

The vacuum pump is activated.

2.

The cargo liquid is suctioned through the following passages according to the degree of vacuum increase.
Suction pipe (3) -> Pump suction inlet (4) -> Main impeller (5) -> Water-air separating impeller (6) -> Bleed pipe (1) -> Float valve (2)

3.

When the liquid flows into the float valve (2), the buoyancy of the float opens the air valve located above it.

4.

When air enters through the air valve, the liquid returns to the main pump and is prevented from flowing into the vacuum pump.

5.

The main pump is activated.

6.

At this point, although there is air remaining in the suction pipe or main pump, the liquid returns to the pump suction inlet (4) through the return passage (7) due to the water-air separating action of the water-air separating impeller (6), so that only air flows into the vacuum pump side.

7.

When the air in the main pump has been completely removed and operation is stable, the vacuum pump stops. However, it reactivates when the sweeping operation (stripping) starts.

8.

In the sweeping operation, some air is suctioned and mixed into the liquid, but most of the air is concentrated at the center of the main impeller (5).

9.

Since the accumulated air is exhausted by the vacuum pump through the holes located in the main impeller (5) and water-air separating impeller (6), the sweeping operation can be performed by continuous bleeding. As a result, suction can be maintained until the bottom of the tank is visible.


The Enhanced Self-Priming Pump in operation
The Enhanced Self-Priming Pump in operation
(Main pump at the rear, Vacuum pump in the front)


Using the Enhanced Self-Priming Pump effectively

The following is a comparison of the Enhanced Self-Priming Pump and a common gear pump.

 

Enhanced Self-Priming Pump

Gear pump

Installation location

It is possible to install either on the deck or bottom of the ship.
It is advantageous to locate the pump on the deck when handling toxic liquids.

Equipped on the bottom of the ship.

Safety

Stable performance and a high degree of safety are ensured since the impeller diameter and the rotation speed dictate the pressure inside the centrifugal pump.

A safety valve is an absolute requirement because the pressure can rise without limit, possibly causing a serious accident.

Discharge rate adjustment

It can be adjusted freely using the valve.

The discharge rate is stable and cannot be adjusted.

Cost

The pump itself is expensive, but maintenance costs are low since the centrifugal pump has fewer malfunctions.

The pump itself is inexpensive. Since the structure consists of gears that contact each other to pump the liquid, the gears are considered as expendable parts, and this results in large expenditures for replacement.

Pumped liquids

Liquids with a specific gravity of 1.4 or less. For high viscosity liquids, the possibility of cavitation must be considered.

Any liquid can be pumped.


The Enhanced Self-Priming Pump, of course, is not for general-purpose use. It should be used properly by considering the above advantages and disadvantages.

1.

The strongest advantage of the Enhanced Self-Priming Pump is that it can be located on the deck. When changing the pumped liquid, the pump or tank needs to be cleaned, so if the pump is equipped on the deck, it is safe and easy to perform the work when dealing with toxic liquids.

2.

Since the Enhanced Self-Priming Pump is a centrifugal pump, the impeller diameter and rotation number dictate the pressure, so that stable performance and a high degree of safety are ensured. However, since the pressure of a gear pump rises without limit, the piping might be damaged if the safety valve does not operate properly.

3.

The discharge rate of the Enhanced Self-Priming Pump can be adjusted with the valve and this proves very useful when loading and unloading liquids. However, the gear pump cannot be adjusted.

4.

In terms of cost, a centrifugal pump is slightly more expensive than a gear pump, but in terms of maintenance, the centrifugal pump has fewer malfunctions and only the packing or ball bearings, which are inexpensive parts, require replacement. Therefore, it is a pump that can be used inexpensively.
The gears in a gear pump are expensive and easily damaged, and four of them must be replaced at the same time when replacing the mechanical seal. Therefore, the gear pump is expensive due to the amount of maintenance required.

5.

In terms of pumping liquids, since the Enhanced Self-Priming Pump is a bleed type, it can handle highly volatile liquids, but as long as the specific gravity is 1.4 or less.
The gear pump can handle heavy or high viscosity liquids.
Therefore, it is important to decide whether to install a gear pump just for handling heavy liquids a few times a year or to install a centrifugal pump and handle light liquids only.



For details of this product, please refer to Enhanced Self-Priming Pump UPM, UPS types.


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