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Product Q&A

Safety and Relief Valve

Are there safety valves with less leakage from the valve seat?

We recommend AL-150T Series and AL-140T Series since both are with excellent airtightness. For O-ring used for valve seat, its material can be changed according to kinds of fluid.

Are there safety valves with superior corrosion resistance?

We recommend the AL-150 Series safety relief valve, in which SCS14A is used for the valve and valve seat.

Material of the safety relief valve we use now has valve and valve seat made of SUS304. We are anxious about this valve because we use it for corrosive fluid.
Are there any products superior in corrosion resistance?

For the AL-150 Series safety relief valve standard product, SCS14A (equivalent to SUS316) with superior corrosion resistance is used for the valve and valve seat.

What are the differences among safety valves, safety relief valves and relief valves?

A safety valve is mainly adopted to ensure safety of a vapor (steam or gas) generator. It is actuated instantly and automatically in case the vapor pressure exceeds the specified value (Referring to JIS B 8210). A relief valve is used to relieve excess liquid (water / oil) pressure. It is automatically actuated to open depending on the pressure increase, in case the liquid pressure reaches the set pressure.
A safety relief valve is mainly installed in a piping system, and it can be used for both gas and liquid.

Please explain about the back pressure at the outlet side of a safety valve.

There are two kinds of pressure at the outlet side of a safety valve.
1. Accumulated back pressure (Pressure at the outlet side of the valve, which is generated by the flow at the outlet side when the valve starts to blow.)
2. Existing back pressure (Pressure which already exists before the valve starts to flow. The pressure is generated by the other sources of supply).

When the back pressure generated as the valve starts to blow exceeds the permissible value (approximately 10% of the blow out pressure), the activation in closing is badly influenced. JIS B 8210 requires deciding the back pressure of blowing pipe according to a safety valve which has a limit of the lowest back pressure.

What is the difference between a lift type and a full bore type?

For the lift type safety valve, a lift of valve seat is more than 1/40 or under 1/4 of an inside diameter of a valve seat opening, and a flow passage area (a curtain area) of valve port becomes the smallest in flow passage area when a valve disc opened.
For the full bore type safety valve, the flow passage area at valve seat is bigger enough than the nozzle throat area at the inlet side.
The lift type is available as AL-XX series, and the full bore type as AF-XX series.

Is there any standard for selecting a safety valve for warning installed at the outlet side of a pressure reducing valve?

There is no regulation specified in the applicable law in Japan,
however, the blowout capacity of the valve should be about 10% of the rated flow of the pressure reducing valve.
As for the set pressure, please refer to the following table.

Are there any other products with higher tightness (of the valve seat) than a safety relief valve for liquid?

The safety relief valve equipped with an O-ring is available, using a soft seat for the trim parts to provide the valve seat with excellent tightness. (Model: AL-150T/-150TR/-150TML/-140T)
For oil use, please contact us for further information.

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