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White Paper: Pressure Transients in Propulsion Tank Pressurization Lines

Posted on Oct 11, 2017 in White Papers |

Published on: Oct 2, 2017 By: Valcor Aerospace Pressure Transients in Propulsion Tank Pressurization Lines Vitor Cardoso – Assistant Chief Engineer, Aerospace Products Richard Kelly – Senior Project Engineer, Aerospace Products Yuri Gerasimov – Chief Engineer, Aerospace Products Abstract Water hammer is a much studied and well known phenomenon. Water hammer is usually associated with pressure surges that can occur in propellant feedlines during engine startup and shutdown. These pressure surges can be the cause of structural damage if they exceed the proof pressure rating of the system. Although much has been done to study the effect of water hammer in propellant feedlines, often the effects of transients in the helium tank pressurization lines is overlooked1. This could be since pressure surges are not always associated with gases. Large solenoid valves have been replacing pneumatic regulators for propellant tank pressurization. These valves are used to create a “bang-bang” pressurization system. Multiple solenoid valves are connected in parallel to create a “bank”. All the same size valves are used in the bank, however they each have a different size flow control orifice installed in the outlet of the valve to provide different flow rates. Each valve is cycled open and closed, as determined by the control scheme, which is maintaining a fixed target pressure in the propellant tank, as the flow demand is changing during flight. These helium flowrates can be large enough to cause significant pressure spikes, as these solenoid valves are suddenly opened and closed. It is for this reason that it is prudent to investigate the pressure transients in the helium pressurization lines, and the analysis presented herein should always be performed on any newly designed aerospace propulsion system. Introduction Historically water hammer was first studied for systems with instantly closing or opening valves. The first person to describe this effect was the Russian scientist Joukowski, who is responsible for the formula for pressure rise, which bears his name. The theory of water hammer was further expanded by the works of Allievi and Gibson, who are both responsible for the calculating the pressure response due to linear stroking valves2. However most of these equations are written for incompressible flow and do not apply to compressible flow, especially sonic flow. To date, a large amount of work has been performed on the subject, and there are many commercially available water hammer software packages that will solve almost any problem1. The purpose of this paper is to show the importance of the need to combine the line dynamics model with the solenoid valve model, since the time history of the valve poppet directly controls the resulting pressure rise. In doing so, we will present a simplified approach to combining...

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White Paper: Instrumentation Cryogenic Valves

Posted on Sep 7, 2017 in News & Events, Product News, White Papers |

Published on: Oct 16, 2017 By: Louis J. Arcuri, Director of Sales & Marketing, Valcor Scientific Instrumentation Cryogenic Valves — Their proper design and application Questions? Contact Us! Name * E-Mail * How can we help you? Cryogenic media enhance our daily lives in so many ways. Our most frequent encounter with the byproduct of cryogenic gas usage is in our food chain. Much of the frozen food we buy is flash-frozen in cryogenic freezers that use liquid CO2 (LCO2) and more commonly, liquid nitrogen (LN2). Vegetables, poultry, fish, and beef are all flash-frozen in immersion cryogenic freezers. Commercially baked goods are cooled much more quickly, and ready for packaging using LN2 vapor. Frozen ice cream novelty treats are flash-frozen in an LN2 bath. Beverages like beer, soda, and sparkling drinks are often carbonated with LCO2 from bulk storage systems. Cryogenics are popular because they’re effective, relatively inexpensive, and don’t affect the color, taste, or flavor of the foods and beverages with which they come in contact. With the advent of microbulk systems, cryogenic cooling is available to more food and beverage processors than ever before, especially small customers who could otherwise not afford the large bulk tanks often seen outside of large-scale producers. Environmental test chambers use solenoid valves to control the flow of LN2, enabling testing at temperatures to -320° F. Environmental chambers are used for testing all manner of components, devices, and systems. They can simulate the cold of deep space; or arctic ambient conditions. Combinations of cryogenic gases are used for a type of surgery known as cryosurgery. LN2 is directly applied to many skin maladies for freezing and removal such as warts, moles, and skin tags. Liquid Argon (LAR) is often used to create a freezing point at the tip of a probe. LAR treatments include freezing of tumors and cancerous tissue. Cryoablation prevents arterial fibrillation in cardiac patients. Cryofreezing minimizes damage to the surrounding healthy tissue. LCO2 is frequently used for cleaning and deburring. CO2 snow cleans surfaces quickly and efficiently, leaving no residue behind. CO2 cleaning is frequently used in optics manufacturing, painted surface preparation, and some semiconductor devices. Dry Ice, or frozen CO2, is used as an abrasive to deburr parts that are too delicate for traditional glass beading or sand blasting techniques. CO2 is also a great solvent; it is often used in a supercritical state to extract the essential oils that are associated with flavors and fragrances. It is also used to decaffeinate coffee and tea, and in sometimes to dry clean fabrics! Finally, we all enjoy the special effects created by LCO2 fogging machines! Whether at a rock concert, or on a Broadway stage, the low-hanging CO2 fog...

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Troubleshooting Reed Switches Used In Valve Position Indication

Posted on Nov 9, 2015 in News & Events, White Papers |

Published on: November 9, 2015 By: Valcor Nuclear Troubleshooting Reed Switches Used In Valve Position Indication Introduction A common method to provide remote position indication in solenoid operated valves (SOV) is to use non-contact reed switches in conjunction with a permanent magnet. This article describes some common issues experienced with non-contact reed switches when used in these systems, and how to diagnose and fix the problems. As part of a position indicating system in SOV’s, reed switches are normally mounted in parallel to a moving armature that has a magnet mounted to one end. In SOV’s, this armature can sometime be referred to as the “plunger”. When the valve is operated, the plunger and the magnet move in parallel to the stationary reed switch, and as the magnet travels it will move “in” and “out” of the sensing area (or range) of the reed switch. When it is in the sensing range, the magnetic force from the magnet will cause the clapper in the reed to make contact or “close”. When the magnet it is out of the range, the clapper in the reed switch will move back to the “open” position. Background Standard non-contact reed switches used in position indication systems have Tungsten contact surfaces, good for 120 DC/AC voltages, and can handle up to 100 watts DC maximum. The standard pull-in range (the value that initiates the movement of the clapper to the closed position) is approximately 40-110 Ampere Turns. The lower the number of Ampere Turns for a switch would indicate the higher the sensitivity for that switch. In measuring the resistance of a switch, the switch manufacturer first determines the minimum Ampere turns to pull-in for the switch, then adds 50% margin to that minimum pull-in. For example, if the pull-in for a switch is 80 Ampere Turns, a value of 120 Ampere Turns is used to close the switch. At this point, an electrical circuit is used to measure the resistance of the switch from the ends of the switch leads. This electrical circuit is powered by a minimum of 10 volts. A typical acceptable Initial Contact Resistance is 0.5 Ohms measured at room temperature between the leads. The manufacturer of the switch recommends that devices like a multi-meter should not be used to measure the resistance of a reed switch, as this can introduce an oxidation or film on the surfaces of the tungsten contacts. This film can raise the resistance of the switch dramatically, upwards to 200 ohms. If a multi-meter is used, the switch should be powered in a circuit at the time of the measurement. Generally, the resistance of a reed switch will increase with temperature. The magnetic force of...

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New Brochure on the Nuclear Group’s Capabilities is Now Available!

Posted on Mar 6, 2015 in News & Events, Product News, White Papers |

Published on: March 6th, 2015 By: Valcor Nuclear Valcor’s Nuclear Product Group has just released its brand new capabilities brochure. Within its pages you can get a feel for the vast capabilities of this group and the years of experience behind the products. You can download the pdf version here. If you would like to request a print copy, kindly fill out our contact form here and mention the brochure in the questions/comments section. Valcor Nuclear provides high quality flow control devices to the nuclear power industry including nuclear power plants, laboratories and waste treatment facilities. For decades, Valcor has earned a reputation of dependability with an expansive installed base of valves and related components in the US and international nuclear market. About Valcor Valcor Engineering Corporation (www.valcor.com), founded in 1951, designs and manufactures solenoid valves and control components for liquids and gases in critical applications in the aerospace, nuclear, light industrial and scientific industries. Headquartered in Springfield, New Jersey, Valcor’s world-class staff of engineers, designers, and technical support personnel utilize fully-equipped, modern test facilities to test the most precise and exacting standards. With a library of more than 18,000 designs, Valcor’s design team can modify existing technology to suit practically every hard to handle application. Valcor specializes in custom applications and can create an entirely new product to meet your needs. For more information, contact Jennifer Eckert of Valcor Engineering at 973-467-8400, ext. 7228 or email...

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Commercialization of Space

Posted on Sep 25, 2014 in News & Events, White Papers |

Published on: Sept 25, 2014 By: Valcor Aerospace Commercialization of Space Provides Opportunities for Innovation: The Use of Permanent Magnets The commercialization of space in the United States has created a competitive market in a sector where qualified, incumbent designs were, previously, difficult to displace. The creation of new rocket systems has driven newer and more innovative designs. These designs also carry with them valuable ‘lessons learned’ from their predecessors. Valcor Engineering has recently had opportunities to create innovative and competitive solutions. One such design is a pilot-operated, pressurization valve that is utilized on first stage rockets. The challenges of designing a component for first stage performance are manifold. Weight, vibration, temperature, leakage, response time and envelope drive the design. Often times, these requirements are in direct competition of each other. For example, a high vibration environment requires a high holding force for dynamic components. This directly affects valve weight and envelope. Large temperature ranges can limit material selection, which can preclude certain design approaches. The piloted valve offers fast, repeatable response time with minimal weight in a high vibration environment. There are many facets of the design that are innovative, but this paper will focus on the use of permanent magnets. Permanent magnets offer several advantages when integrated into solenoid designs. Specifically, reduced power consumption, lower weight, and the ability to withstand high vibratory environments. For this particular design, permanent magnets were integrated into the pilot solenoid assembly as an approach to address a high vibration environment. In a typical spring-mass system, the spring and mass will have a response to any outside excitations. There are challenges to ensuring that the natural frequency is outside of the vibration spectrum. If the spring-mass system displacement becomes large or achieves resonance, then the valve may leak or fail. For this design, the mass is the pilot plunger and the spring is the holding spring. Simply increasing the spring force to increase the required holding force will directly increase the valve solenoid weight and size, because the solenoid must overcome this larger spring force. Furthermore, the valve plunger diameter needs to increase to prevent magnetic flux “choking.” However, there is a saturation point reached for the magnetic material of the plunger and thus any additional increases in plunger diameter are not beneficial. These changes will increase the mass portion of the spring-mass system and the resulting valve design becomes untenable. Enter the Permanent Magnet When a permanent magnet is introduced into the magnetic circuit it will add additional plunger holding force without adding to the pull-in force requirements of the solenoid, and thereby not increase the plunger diameter. This will increase the maximum vibration envelope that a plunger-spring system can withstand....

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White Paper: Solenoid Valve Leakage

Posted on Sep 9, 2014 in News & Events, Product News, White Papers |

Published on: Sept 9, 2014 By: Valcor Nuclear A White Paper on Solenoid Valve Leakage — Identifying Root Causes and Methods for Eliminating Leakage Leakage in solenoid valves are classified as external and internal. External leakage is generally easy to identify and eliminate. The majority of external leakage comes from degraded O-ring seals, either worn out from usage or incorrectly installed. The solution to eliminate this leakage is to correctly install a new O-ring. Solenoid valves that use diaphragms as a sealing member can also experience external leakage via wicking through the diaphragm. Wicking is a process whereby the pressurized fluid journeys through the diaphragm material between the rubber and reinforcing material of the diaphragm. Solutions to eliminate wicking would be to use a non-reinforced diaphragm (or solid diaphragm), or use anti-wicking compounds of the diaphragm material. The focus of this white paper will be on internal leakage, or often termed, seat leakage. Internal leakage is defined as the process fluid passing through between the valve seat and sealing member (Obturator) when the valve is in the closed position. The obturator or disc can be either soft (elastomeric), or hard (metal to metal). When specifying seat type, the factors to consider when determining what type of seat material to be used are: Process medium differential pressure, temperature, Fluid type (gas versus liquid), Process medium composition (chemical resistance and fluid compatibility with seat material) Customer preference/specification. The effects of seat leakage can range from just an annoyance in non-critical applications to damaging in systems that cannot tolerate any amount of leakage. In any case, seat leakage is generally not an acceptable condition. However, there are some cases where a design specification will allow for certain leakage rates. This is typical in metal to metal or hard seating constructions. What are the causes of seat leakage? Normally, the main cause of seat leakage is foreign materials in the process medium. Particles in the medium become trapped between the seat and the sealing disc causing seat leakage, either by creating a gap between the parts or creating an indentation or cut in the parts. Typically, these seat leakages start out small. However, depending on the process fluid and the pressure of the fluid, a small leakage can escalate quickly to a high leakage rate. In these cases, the surfaces of the seat and disc can erode in ways like steam flashing and high velocity erosion. The high velocity of the liquid traveling thru the leakage path can erode the sealing surfaces, eventually leading to a high rate leakage and/or failure. The installation of the valves into the piping system, whether by NPT threads or welding, can introduce foreign materials. Pipe tape or...

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