Non-Water Hammer Check Valve

Non-Water Hammer Check Valve
SL series (PAT.)

No valve closure delay means no water hammer and no noise

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

Bore	40-1000mm
Rated pressure	1-2MPa

>Selection & Dimensions

The YOKOTA Non-Water Hammer Check Valve is a high performance check valve that safely and economically eliminates the danger of water hammer which is a major problem in pumping and water supply equipment.

Mining of underground resources such as coal, from hundreds of meters underground involved contending with a large amount of water. If a pump stopped operating due to a power failure, intense water hammer would occur causing an accident that could lead to pipe ruptures, pump damage, and even put the lives of workers in danger.
The YOKOTA Non-Water Hammer Check Valve clearly solved this problem.

Since then, the valve has been widely adopted in many public facilities such as water supply pumping plants, pumping stations, supply pipelines, agricultural irrigation, and sewage systems. With buildings being built higher and various types of equipment requiring higher pressure, a solution to the water hammer problem has become increasingly important, and we have developed a good reputation through our many achievements in this field. Also, many of our clean-finished Non-Water Hammer Check Valves for ultra-pure water are used in the semiconductor industry.

	No water hammer
	Due to the patented construction of the valve which opens and closes in response to water flow, there is no delay in valve closure and water hammer does not occur. The valve operates quietly and fits well into quiet surroundings.
	Superior characteristics
	Head loss of the valve is equivalent to JIS swing check valves and the valve is adaptable to a variety of applications.
	Easy to handle
	Even the large valves feature simple, single-disk construction that eliminates breakdowns so maintenance costs can be reduced considerably.
	No-Feed Detector
	The valve can be equipped with the accurate No-Feed Detector (except SL-UC, NU types) facilitating the safest possible automatic pumping.

Non-water hammer principle (PAT.) ....

The YOKOTA Non-Water Hammer Check Valve adjusts to the flow so that there is no valve closure delay and water hammer does not occur.

Phenomenon of water hammer

In a pumping system without a check valve, when pump input stops suddenly, the flow in the pipe goes through stages of "normal rotation, normal flow", "normal rotation, reverse flow", and "reverse rotation, reverse flow" and reaches a stable state. In such a case, the maximum pressure increase reaches 150-160% of the total pump head, which is comparatively small. However, check valves are normally installed in actual pump systems, and the situation is entirely different.

Condition in pump immediately after power failure
(without check valve)

Conventional check valves

With conventional check valves, there is a tendency for valves to begin to close only when pressed by reverse flow. Instantaneous stoppage of reverse flow causes pressure to rise resulting in a water hammer noise similar to striking a pipe with a hammer, and in some cases, this causes a blowout in the discharge line.

Concept of the YOKOTA Non-Water Hammer Check Valve

Non-Water Hammer Check Valve / Phenomenon of water hammer

The YOKOTA Non-Water Hammer Check Valve

Water hammer does not occur.
According to our patented non-water hammer principle, the valve disk of the YOKOTA Non-Water Hammer Check Valve is designed to be submerged in, and suspended by the water flowing in the pipes during maximum flow. When normal flow begins to slow down, the valve disk begins to close in response to this. The instant that flow reverses, in other words, when the water in the pipe stops, the valve disk closes completely and water hammer does not occur. This is similar to the shock eliminating effect of a ball that is thrown upward and caught at the moment when it begins to fall.

Comparative test....Pressure change with time after pump operation is stopped

YOKOTA Non-Water Hammer Check Valve

Test equipment

Type of pump:	Self-priming centrifugal pump
Pump specification:	12m³/h x 50m x 3500min^-1 x 7.5kW
Discharge pipe:	40mm SGP13m
Recording paper feed rate:	50mm/sec

Conventional check valve

We are holding an "Online Exhibition" where you can experience the same kind of tour as a real exhibition on the web.
In addition to the Non-Water Hammer Check Valve, we are exhibiting many videos that are based on actual examples, including operation examples of various pumps and valves such as defoaming/degassing pumps, and evaluation methods of operation results.
(> "Online Exhibition" page)

Non-Water Hammer Check Valve SL series

Example applications

For sewage treatment plants

For water purification plants

Sapporo City Sewage Department
SL-SH-1000

Non-Water Hammer Check Valve / For water purification plants

SL-SN-400B

For iron and steel works
>"Current Topics: Steel Works"

For undersea tunnel drainage
>"Current Topics: Undersea Tunnel"

Non-Water Hammer Check Valve / For iron and steel works

SL-SH-600


The Kanmon Tunnel SL-NBP-200	The Seikan Tunnel SL-SN-300 (JIS 30K)

For aquariums
>"Current Topics: Aquarium"

For seawater intake
>"Current Topics: Seawater Intake"

Non-Water Hammer Check Valve / For aquariums

SL-SN-150

Shrimp hatchery
SL-SN-200

For power plants
>"Current Topics: Slurry Self-Priming"

For chemical/electronic industry

Non-Water Hammer Check Valve / For power plants

SL-NU-200

Non-Water Hammer Check Valve / For chemical/electronic industry

SL-SN-250

For river water intake
>"Current Topics: Snow Removal"

For agricultural irrigation
>"Current Topics: Irrigation Supply"

Non-Water Hammer Check Valve / For river water intake

SL-NB-200

Non-Water Hammer Check Valve / For agricultural irrigation

SL-SN-250

The valve can be applied for use with various kinds of liquid ranging from pure water to seawater, contaminated water and chemical liquid as it can be made from YOKOTA's duplex type stainless steel YST130N with high corrosion resistance.
For details of YST130N, please refer to this page.

Examples of non-water hammer pumping systems

Solution to water hammer caused by simple reverse flow (Eliminated with only the Non-Water Hammer Check Valve)
	With coil spring

Solution to water hammer caused by recombined flow after water column separation
(Surge tank is not required because of patented non-water hammer principle)

Non-Water Hammer Check Valve / Examples of non-water hammer pumping systems

Please note the following points when installing the Non-Water Hammer Check Valve.

1	Do not install with the discharge side facing downward.
2	Do not install with the discharge side facing downward.
3	SL-SN, SH types must not be installed in a leaning position.
4	The check valve must not be exposed to any deflected flow directly after the pump or other valve.
5	If air is trapped in the pipe before the check valve, chattering may occur when starting pump operation. Make sure to install an exhaust valve in such cases.
6	If the check valve on a submerged or vertical pump is installed at ground level, the inlet side of the check valve may become a vacuum when the pump is stopped and may cause water hammer. Carefully plan the location of the check valve in such cases.
7	In addition to water hammer directly after the discharge of the pump, examine surging due to negative pressure in the middle of piping. (Please contact us for details.)