Safety valve Model 64
General features
Model 6400, is an angular type safety valve at 90º between the inlet and the outlet connections, with flanged connections, full nozzle, direct action and spring loaded. Subdivided into three types: Conventional, Balanced (with bellows) and Balanced-Piston. All three are designed with specific trims to work with gases and vapours or liquids.
DESIGN
• Valve body is angular type at 90º between inlet and outlet flanges. Its large internal capacity and smooth section changes help reduce turbulences. Therefore, fluid evacuation on discharge is improved.
• Full nozzle type, guided and screwed to body, enabling perfect alignment and easy disassembling.
• Disc is separate from disc-holder, for that reason its repair or change is improved and a better selection of materials can be performed.
• Stem-push rod design in two parts, enables push rod material to be hardened to withstand high charges, facilitating displacement,
avoid seizure with guide.
• Guide has a large push rod guide area to prevent premature damage, demonstrating perfect alignment with all internals.
• Bellows are performed so its average area is equal to orifice area thus achieving perfect valve balance and consequently perfect
operation before variable back pressures. Its meticulous design enables maximum pressures and temperatures to be supported
achieve a high degree of elasticity.
• Springs are designed with an experimented highly reliable calculation software and manufactured with the ideal material qualities for the process conditions, enabling and accurate repetition of valve opening.
• For design of the different valve types has taken into account standardisation, enabling a conventional type valve to be converted into balanced with minimum parts change.
CODES AND STANDARDS
Valves have been designed and manufactured in compliance with the following directives, codes and standards:
European Directive: | 97/23/CE (PED) |
European Directive: | 94/9/CE (ATEX) |
Design: | EN ISO-4126-1 & ASME VIII DIV-1 |
Certifications: | PED MODUL B+D / ASME “UV” & “NB” |
Pressure and Temperature Limits: | API-526 & ASME 16.34 |
Tests: | API-527 & ASME 16.34 |
Quality system: | EN ISO-9001:2008 |
Materials: | ASTM/ASME & EN |
SIZES AND RATINGS
Standard sizes and ratings:
ANSI: | |
Sizes: | 1”x2” up to 12”x16” |
Rating: | 150# up to 2500# |
EN/ISO: | |
Sizes: | DN-25xDN-50 up to DN-300xDN-400 |
Rating: | PN-10 up to PN-420 |
•This catalog reviews standard valves. Upon request, our technical department can design special applications.
•The safety valve is an automatic direct action accessory whose function is to relief excessive overpressures in the recipients and installations that protects. Its main characteristics, allows its sudden fluid discharge with complete and fast opening (pop).
•Automatic valve opening is produced because of the additional push provided by the overpressure of the fluid itself helping to over- come spring resistance. Once the installation has recovered its normal service condition, the valve closes again.
•Safety valve behavior is totally different according to whether the fluid it works with on the installation is in gas or liquid phases. To achieve good valve functioning and correct dimensioning, this model was designed with internals for working with gas (Type-64G ) or liquid (Type 64L )
OPERATION
The safety valve which protects a pressurized recipient or installation, remains closed until the force exerted by the pressure of fluid P1, against the disc, is equal to the force of spring Fr. (Fig.1). From this point of equilibrium, the disc holder comes away the nozzle, releasing a small amount of fluid, (valve set pressure) which is integrated in the ring chamber (C) formed between the disc holder and adjusting ring (Fig. 2). Chamber pressurization (C) creates an additional force contributing to total instantaneous valve opening (Fig.3). Maximum valve elevation must be achieved without the installation exceeding 10% of overpressure, regardless of whether fluid is in gas or liquid phase.
Once cause creating the overpressure has dissapeared, pressure will reduce in the installation to a certain value bellows the set pressure, leaving the valve completely closed. The difference between set pressure and re-seating pressure (blowdown), may be between 7% and 15% depending on whether valve works with gas or liquid.
OPERATION AT CONSTANT BACK PRESSURE
When a conventional safety valve (without bellows) Type 64 C, is installed in a location where fluid discharge is performed on a pressurized collector, with constant pressure ( P2), one must take into account this back pressure value. This back pressure influences on the upper and lower disc holder surface, remaining balanced except for the bottom area occupied by the inlet orifice valve ( Sa ) where back pressure does not act. This decompensation results in an additional force added to the spring effort. Therefore, at the time of adjusting valve pressure on the test bench, one must subtract from set pressure ( P1 ), the constant back pressure ( P2 ). If the valve is balanced (with bellows) Type 64 F, correction is not necessary as detailed bellow.
OPERATION AT VARIABLE BACK PRESSURE
If conventional valve Type 64 discharges fluid into a collector where back pressure is variable, then the set pressure is affected by the same variation. If this variation is inadmissible (10% greater than set pressure), a balanced valve (with bellows) Type 64 F must be installed.
Bellows function is to eliminate effects caused by back pressure.
As bellows mean diameter area ( Sf ), equals the valve inlet orifice area ( Sa ), it isolates the disc holder upper surface from back pressure action, setting it to atmospheric pressure through the vent hole in valve bonnet. As decompensation of areas produced in conventional valves is eliminated, additional efforts on the spring are eliminated. Therefore, when the valve set pressure is adjusted on the test bench, no back pressure correction at all is required.
BACK PRESSURE EFFECT
When valve initiates opening under back pressure influence due to built-up back pressure or superimposed back pressure, two conditions occur preventing the valve from achieving total elevation without exceeding 10% overpressure: The force on the upper disc holder surface, and pressure reduction on the lower disc holder surface due to disturbances generated on discharging fluid.
Back pressure data indicated on the operation technical table, are experimental back pressures performed in laboratory on different valve types, and at no time exceed the maximum overpressure of 10%
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