Euler's Law of Compressed Columns determines the buckling point of the pin. It states the axial force causing the pin to buckle is proportional to the pin diameter to the fourth power times the pin material Modulus of Elasticity divided by the pin length squared. By using Euler's Law, the pin's diameter and length can be determined, and the set point accurately predicted, every time. In order to keep pin dimensions precise and insure set point accuracy, we control the pin diameter to five decimal places and the length to four decimal places. The modulus of elasticity of the pin material is the only variable affected by ambient temperature. Using materials that have a very minimal change in modulus of elasticity over the ambient temperature range of the valve exterior solves this challenge. One pin alloy used has a modulus of elasticity variation of .3% over a temperature range of –200°F to +400°F. Because the pin is in compression and always below its elastic limit, pulsation is not a factor and the pin can never fatigue. Since the pin is external to the system fluid, pin corrosion is not a concern. The ambient environment is no problem since the pin is made of non-corrosive alloys.
MULTIPLE CAPABILITIES
• There are very few limitations to valve sizes or set points.
.....Pressure set points can be set as low as 1 psi to as high as
.....50,000 psi and vacuums as low as 1 psi.
• Buckling Pin valves can be designed to effectively handle
.....corrosive and dangerous fluids and gases with no
.....environmental concerns, because the systems' integrity
.....is not compromised when resetting the Buckling Pin Valve.
• Buckling Pin valves can be made of special alloy materials,
.....plastics or have glass lining to meet your special requirements.
• The valves may also be equipped with a proximity switch to
.....alert a remote operator that the valve has closed.
• Replacement pins can be stored at the valve.
• The Buckling Pin valve can have multi-action capabilities by using
.....3-way or 4-way ball valves instead of piston or plunger valves.
VALVE CERTIFICATION TESTS INSURE ACCURACY
Certification tests are done on all valves before they leave our facility. The ASME standard calls for set point variation of +/–5%. Our valves often achieve +/–1% and rarely exceed a deviation above +/–3% from set point. After successful valve testing, three pins are tested on our Tinius Olsen machine to determine a load vs time curve independent of valve seal friction. The results are archived. This insures consistency between pin material lots. Custom methods are used to achieve accurate set points with material batch changes.
Special machines are used to cut the pins to an exact length perpendicular to the pin axis and polish the cut ends. All pins are tagged with all pertinent information required to match the pin to the valve. All valves have a serial number stamped on the bonnet and valve label. New Pins may be ordered just by using the valve serial number. Some Buckling Pin ESV models have color coded pins to insure the proper set pressure. Pins ordered before 12:00 pm CST on business days are shipped the same day.
APPLICATIONS
Buckling Pin Valves have many uses where instant emergency shutdown at setpoint is required. Where you are now using a pressure relief valve or rupture disk, an ESV may save you operational expenses and eliminate environmental concerns.
Industry must change present operating procedures and limit the use of conventional relief valves and rupture disks. Every time a relief valve opens or a rupture disk bursts, you have potential pollution entering the atmosphere. Even though you use a flare system, you are changing combustible fluids to CO and CO2. A Buckling Pin emergency shutdown valve isolates excess pressure to keep it from reaching protected systems. This eliminates the need to discharge excess pressure.
An example of this is high pressure gas going to a chemical reactor or containment vessel through a pressure reducing regulator. Assume the regulator malfunctions and fails open. You now have high pressure moving to overpressure downstream systems. Conventional design would dictate a large relief valve to vent and flare the excess pressure until the flow is stopped and the faulty pressure regulator is replaced. The proper method is to isolate pressure from the faulty regulator with a self-contained emergency shutdown valve. This eliminates the need to vent to atmosphere until the source is shut off and the regulator replaced. If the flow is going to a low pressure vessel, you may require a small thermal relief valve downstream – one that does not require a flare system.
SUMMARY
Protect elements that would be affected by a connecting pressure upset by isolating the pressure surge with a proven Buckling Pin emergency shutdown valve and protect elements at the surge source with a reliable Rupture Pin relief valve. For more on Rupture Pin relief valves, visit http://www.rupturepin.com
For additional information on Buckling Pin valves, contact Lee Levisay at (405) 789-0534 office or (405) 830-0776 mobile.
(405) 789-1942 Fax • 8226 SW 8th, Oklahoma City, Oklahoma 73128
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The simple maintenance consists of assurance that the piston moves freely. Here are two ways to check the piston movement.
1) Remove the pin and apply pressure to the valve of no more than 10-20% of the set point. If the piston moves, the valve is in good operating condition. The pin obeys Euler's Law and is never a concern.
2) To test while in operation, turn the pin holding nut one quarter to one half turn counter clockwise - no more. If the piston moves, the valve is in good operating condition. Tighten the holding nut clockwise. If the piston does not move, remove pressure from the valve. Remove the top assembly by removing the bonnet bolts. (The top plate should never be removed from the bonnet.) Remove the piston and replace the elastomer o-rings; reassemble. Check to make sure the pin is not damaged or bent by rolling on a flat service. The pin must roll evenly with no wobble. |
