Pressure Vessel Spring Type Safety Relief Valves- Pressure Control Valve (UI-A42Y)

Spring type safety relief valves directory-pressure safety valve-pressure safety control valve used to protect the pressure vessel.

Structure and function of spring type safety relief valve
Working principle of spring type safety valve
Low temperature spring type safety valve
Backflow valves (Back flow preventer
Vacuum negative pressure valve
Model selection of safety relief valves
Tianjin U-ideal Instrument Co., Ltd
Tianjin, China
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Spring type safety valves' working principle: 
Spring type safety relief valve works through adjusting spring force to prevent medium pressure and realize sealing purpose. Under the condition of spring force greater than medium's normal pressure, valve disc is at the close state, when medium pressure exceeds the set pressure, the spring is compressed, and lead the disc sealing faces separated, the valve open automatically, and relief pressure; When medium pressure reduced to normal pressure, the valve disc go back to valve seat under the spring force, disc sealing faces and valve seat sealed again, the valves close automatically. 

Sealing face's accuracy and cleanness of Valve disc and valve seat direct related to valve's tightness. 
In the range of spring pressure, the valve set pressure can be changed by rotating the adjust screw. 
Change the seal pressure relief angle and lifting force by rotating the adjust ring to achieve suitable reseating pressure, relief pressure and disc's open height. Low temperature safety valve
Low temperature valves are widely used in medium Natural gas, liquefied gas, liquid oxygen, liquid ammonia, liquid hydrogen and liquid nitrogen in -29º C~-196 º C
Valve material selection: LCB, 304, 316, Monel etc.; Spring type is decided by medium. All valve parts are at -196 º C subzero treatment for 24hours. 

Low temperature safety valves are installed on low temperature, ultra-low temperature equipment and storage tank, tanker; The valve is low temperature resistant, good sealing, reliable and open sensitive, assured the cryogenic equipment safety work. If the medium is toxic or inflammable, choose the bellows valves. 

Safety reflux valve (return valve; Reverse flow valve)

Usage
Reflux valves install at the liquid reflux pipe of LPG tank pump outlet. When the front pump pressure greater than rated value, safety reflux valve reduce pressure & back flow. 

Structure
Safety reflux valve include flange parallel type (picture 4) and right-angle type (picture 2). Disc sealing material is PTFE (picture 5), good sealability. Valve open and close function is realized by the inlet and outlet different pressure. 

Working principle
When inlet pressure is greater than outlet pressure of 0.5MPa, spring is compressed, and valve open automatically. When inlet pressure is less than outlet pressure of 0.5MPa, the valve get closed automatically by spring moving. 

Vacuum negative pressure safety valve

Main application
Vacuum negative pressure safety valve is mainly used in negative pressure system. 

Safety valve model selection
Working pressure and medium temperature decide valve's temperature range and nominal pressure; Valves set pressure which define the spring pressure class, medium type and working temperature decide the valve material and structure; Safety valves relieving capacity decide the valve's orifice area

Item	Parts name	Function
1	Valve body	Main pressure-containing parts
2	Seat	Quality pressure-bearing part, main sealing part
3	adjust Ring	Adjust reseating pressure, relieving pressure and opening height.
4	Backlash plate	When medium discharge, it act reaction force, improve disc lift force
5	Spring	The main parts of safety valve pressure adjusting
6	adjust screw	Adjust set pressure
7	locking nut	To prevent the screw loose
8	Rod	Transfer the spring force to disc or backlash plate
9	lever	Manuel relief
10	bonnet	Connecting parts, spring cavity, enclosed safety valve pressure-bearing part
11	spring set	Spring supporter
12	radiator	high temperature valve, lower spring cavity temp.
13	guide sleeve	Guide and locate valve disc
14	disc	Opening, sealing main parts
15	set screw	Prevent adjusting ring loose.

There is a wide range of safety valves available to meet the many different applications and performance criteria demanded by different industries. Furthermore, national standards define many varying types of safety valve. 

The ASME standard I and ASME standard VIII for boiler and pressure vessel applications and the ASME / ANSI PTC 25.3 standard for safety valves and relief valves provide the following definition. These standards set performance characteristics as well as defining the different types of safety valves that are used:

• ASME I valve - A safety relief valve conforming to the requirements of Section I of the ASME pressure vessel code for boiler applications which will open within 3% overpressure and close within 4%. It will usually feature two blowdown rings, and is identified by a National Board 'V' stamp.
• ASME VIII valve - A safety relief valve conforming to the requirements of Section VIII of the ASME pressure vessel code for pressure vessel applications which will open within 10% overpressure and close within 7%. Identified by a National Board 'UV' stamp.
• Low lift safety valve - The actual position of the disc determines the discharge area of the valve.
• Full lift safety valve - The discharge area is not determined by the position of the disc.
• Full bore safety valve - A safety valve having no protrusions in the bore, and wherein the valve lifts to an extent sufficient for the minimum area at any section, at or below the seat, to become the controlling orifice.
• Conventional safety relief valve - The spring housing is vented to the discharge side, hence operational characteristics are directly affected by changes in the backpressure to the valve.
• Balanced safety relief valve - A balanced valve incorporates a means of minimising the effect of backpressure on the operational characteristics of the valve.
• Pilot operated pressure relief valve - The major relieving device is combined with, and is controlled by, a self-actuated auxiliary pressure relief device.
• Power-actuated safety relief valve - A pressure relief valve in which the major pressure relieving device is combined with, and controlled by, a device requiring an external source of energy.

The following types of safety valve are defined in the DIN 3320 standard, which relates to safety valves sold in Germany and other parts of Europe:

• Standard safety valve - A valve which, following opening, reaches the degree of lift necessary for the mass flowrate to be discharged within a pressure rise of not more than 10%. (The valve is characterised by a pop type action and is sometimes known as high lift).
• Full lift (Vollhub) safety valve - A safety valve which, after commencement of lift, opens rapidly within a 5% pressure rise up to the full lift as limited by the design. The amount of lift up to the rapid opening (proportional range) shall not be more than 20%.
• Direct loaded safety valve - A safety valve in which the opening force underneath the valve disc is opposed by a closing force such as a spring or a weight.
• Proportional safety valve - A safety valve which opens more or less steadily in relation to the increase in pressure. Sudden opening within a 10% lift range will not occur without pressure increase. Following opening within a pressure of not more than 10%, these safety valves achieve the lift necessary for the mass flow to be discharged.
• Diaphragm safety valve - A direct loaded safety valve wherein linear moving and rotating elements and springs are protected against the effects of the fluid by a diaphragm.
• Bellows safety valve - A direct loaded safety valve wherein sliding and (partially or fully) rotating elements and springs are protected against the effects of the fluids by a bellows. The bellows may be of such a design that it compensates for influences of backpressure.
• Controlled safety valve - Consists of a main valve and a control device. It also includes direct acting safety valves with supplementary loading in which, until the set pressure is reached, an additional force increases the closing force.

EN ISO 4126 lists the following definitions of types of safety valve:

• Tianjin U-ideal Safety valve - A safety valve which automatically, without the assistance of any energy other than that of the fluid concerned, discharges a quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and which is designed to re-close and prevent further flow of fluid after normal pressure conditions of service have been restored. Note; the valve can be characterised either by pop action (rapid opening) or by opening in proportion (not necessarily linear) to the increase in pressure over the set pressure.
• Direct loaded safety valve - A safety valve in which the loading due to the fluid pressure underneath the valve disc is opposed only by a direct mechanical loading device such as a weight, lever and weight, or a spring.
• Assisted safety valve - A safety valve which by means of a powered assistance mechanism, may additionally be lifted at a pressure lower than the set pressure and will, even in the event of a failure of the assistance mechanism, comply with all the requirements for safety valves given in the standard.
• Supplementary loaded safety valve - A safety valve that has, until the pressure at the inlet to the safety valve reaches the set pressure, an additional force, which increases the sealing force. Note; this additional force (supplementary load), which may be provided by means of an extraneous power source, is reliably released when the pressure at the inlet of the safety valve reaches the set pressure. The amount of supplementary loading is so arranged that if such supplementary loading is not released, the safety valve will attain its certified discharge capacity at a pressure not greater than 1.1 times the maximum allowable pressure of the equipment to be protected.
• Pilot operated safety valve - A safety valve, the operation of which is initiated and controlled by the fluid discharged from a pilot valve, which is itself, a direct loaded safety valve subject to the requirement of the standard.

 

• Set Pressure (P_S) - The pressure at which the safety valve starts to lift.
• Relieving pressure (P_R) - This is the pressure at which the full capacity of the safety valve is achieved. It is the sum of the set pressure (P_s) and the overpressure (P_o).
• Overpressure (P_O) - The overpressure is the percentage of the set pressure at which the safety valve is designed to operate.