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Poppet Style Pressure Control Valve

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Poppet Style Pressure Control Valve Multi-Disciplinary Engineering Design Conference Kate Gleason College of Engineering Rochester Institute of Technology Rochester, New York 14623 Project Number: 06442 POPPET STYLE PRESSURE CONTROL VALVE Gregory Dennis Shukri Elmazi Troy Rutherford ABSTRACT This type uses a tight fitting spool in a precision honed Under the hood valve systems for heavy bore. Spool valves are extremely sensitive to diesel applications often rely on electrical or hydraulic contamination in the working media. They also work systems to actuate. Imagine if you could use an poorly with low viscosity fluids such as air, due to existing media on-board that was intrinsically safe and inherent gap between the components. environmentally friendly. A poppet style pneumatic Poppet style pressure control valves have valve powered by a voice coil actuator would yield a many benefits when compared to spool types. Poppet highly accurate, robust and efficient option to style valves have very low contamination traditional actuation systems. susceptibility, low leakage and the ability to withstand high pressure operation. A typical poppet style INTRODUCTION version utilizes two solenoid operated valves. This is A traditional valve system consists of direct because the design allows for one valve to reduce free electrical and electro-hydraulic actuators. stream pressure at a certain point and the other valve Direct electrically driven valves require to relief pressure from that point. This is undesirable electric motors to create a needed force. This force is because of the increased complexity of the system. created by the direct conversion of electric current into torque. These motors often have a service rating for APPLICATION AND REQUIREMENTS: temperatures up to 200°F (93.3°C). The low The mission of the design team was to temperature rating is the limiting factor for most develop a pressure control valve for a pneumatic motors because of their permanent magnets and application. The poppet style valve was chosen due electrical solder joints. Magnets and high temperature the qualitative aspects. As for operating the valve, a solder exist but are not classically used due to cost voice coil operator was chosen for its high force, high constraints. These limitations cause difficulty in accuracy and low hysterisis. under-hood applications where the typical ambient The pressure control valve will be used temperature exceeds 300°F and per unit cost is a high primarily in heavy diesel truck applications in which visibility consideration. air is the working media. The end users of the valve Electro-hydraulic valves commonly utilize specify the following requirements for heavy diesel engine lube oil coupled with a solenoid operator to truck applications. The valve must endure create a required force. This style of valve is much temperature extremes form -40°F to +450°F (-40°C to more durable in applications exceeding 300°F 232°C) and supply a pressure range of 10psi to 90psi (149°C). This is due to the ability to insulate the (69kPa to 620kPa) with a response time of 50ms. The electrical components from the heat source. Some of poppet style valve coupled with a voice coil operator the limiting factors for a classical electro-hydraulic will accomplish these requirements. valve are flammable working media and a relatively short working stroke. BASIC CONCEPT AND OPERATION: Solenoid force decreases exponentially with increasing A Poppet style valve is used in industry for stroke. If longer stroke is required a solenoid must pneumatic applications due to their low contamination drive a secondary valve to operate the primary system. susceptibility and low degree of internal leakage. Currently many pressure control valves exist However most pressure control poppet valves on the on the market today. One type is a spool type valve. market utilize two separate actuators, effectively two © 2005 Rochester Institute of Technology Proceedings of the Multi-Disciplinary Engineering Design Conference Page 2 valves are used to control pressure at one point. Our design is an attempt to use only one actuator to control two poppets using a creative means of force balancing. Charging Discharging The actuator of choice is a voice coil which will give Linear (Charging) Linear (Discharging) proportionality and zero magnetic hysterisis. Before Pressure vs. Current designing the voice coil, the valve section must be 120 designed to determine the proper force needed. Figure 1 illustrates the valve design and the common parts. 100 ) g i 80 s Relief Reducing p ( Diaphragm Seat Poppet e r 60 Spring u s #1 s e r 40 P 20 0 0 1 2 Current (A) Figure 2. Note the slight difference between the charging Relief Reducing Working and discharging curves. The expected hysterisis Poppet Vent Inlet Seat Port in this design is inherent to the springs chosen. The largest effect on this band is seen in the preload chosen for spring #1. Figure 1. Valve cross section ORIFICE SIZING FOR RESPONSE The first thing to consider is sizing the valve When charging, the relief poppet is pushed by for the required response time. From the requirements the voice coil (not shown in Fig. 1), which comes in listed above we can determine the flow rate to charge contact with the relief seat. The relief and reducing the given volume in the allotted time. This is achieved poppet can be viewed as one mass during the charging by the definition of flow rate as some volume per unit of the valve. The force from the voice coil now acts time. on the reducing poppet. The reducing poppet lifts off the reducing seat allowing airflow into the working ∀ port. The design will use a spring in both the valve Q = (1) and voice coil sections so the unit will have a t preferred orientation which is normally closed in case of system failure. We also know that flow rate can be defined When discharging, the force on the relief by the velocity of a fluid flowing through a specific poppet is reduced by decreasing the current to the cross sectional area. voice coil. This causes a force imbalance between the relief seat and the reducing seat. The pressure in the Q = V * A (2) working port acts on all surfaces between the relief and reducing poppets. Spring #1 and the pressure in The orifice size is relevant to the flow area the common port cause the airflow area to reduce, when the valve is open for charging. In order to find allowing pressure to increase or decrease accordingly. the required orifice size, the area from Eq. (2) is The relief seat remains in contact with the relief required. In order to calculate the area, velocity and poppet not allowing premature venting to occur. After flow rate need to de determined. The following the reducing poppet contacts the reducing seat, the equations are defined and simplified for use. Equation relief poppet lifts off the relief seat causing the valve (3) represents the Ideal Gas Law and Eq. (4) is the to vent. The venting is controlled by the force the geometric definition of a circle. Equation (5) voice coils exerts on the relief poppet. The desired represents Bernoulli’s equation. pressure is achieved by controlling the current to the voice coil actuator. P ρ = (3) RT Page 2 of 8 Proceedings of the KGCOE Multi-Disciplinary Engineering Design Conference Page 3 2 π * deq 3 A = (4) 5in Volume T= -40f 4 Inlet P1=100 psi V1=? 2 2 dv dP 1 2 2 — ds + — + (V2 −V1 ) + g(Z 2 − Z 2 ) = 0 1 dt 1 ρ 2 (5) The following assumptions are made to simplify Bernoulli’s equation: Tank • Charging and Discharging require the same P2=90 psi orifice size. V2=0 • Steady Compressible frictionless flow. • Neglect Heat Transfer. Figure 3. Static volume and flow rate model. • Air behaves like an ideal gas. Using Bernoulli’s equation and simplifying We can now solve for fluid velocity at the Eq. (5) based on our assumptions. inlet. Solving Eq. (9) by using values defined in Fig. 3 with R being the universal gas constant. 2 2 in dP V1 V = 4674.63 (119m/s) Solution 1 — − = 0 (6) 1 s 1 ρ 2 Using Eq. (1) and substituting values we get Substituting Eq. (3) into Eq. (6) in3 2 RT V 2 Q = 100 (1639cm3/s) Solution 2 — dP − 1 = 0 (7) s 1 P 2 Substituting solution 1 and 2 into Eq. (2) Rearranging Eq. (7) A = .02139in2 (0.14 cm2) Solution 3 2 2 1 V1 = 2RT dP (8) This is the equivalent orifice area required in — 3 3 1 P order to charge a 5 in (82 cm ) volume in 50ms. We will need this when calculating the seat diameter and Then integrating Eq. (8) we get. stroke. From the equivalent area we can determine the equivalent orifice diameter from Eq. (4). 2 P2 V1 = 2RT * ln deq = .165in (0.42 cm) Solution 4 P 1 This is the minimum diameter allowable for the ID of the reducing poppet through hole in order to P2 ensure the valve will meet the required response time. V1 = 2RT * ln (9) P1 SEAT DIAMETER SELECTION The main driving factors concerning seat To find V we can model a static volume with diameter are the selection of stock diaphragms, a charged pipe flowing into it. See Fig. 3. The charging pressure of the valve and the desired output pressures in Fig. 3 were selected to represent the case force of voice coil. Since the valve will be charging to where the velocity will be the slowest at the extreme 90psi (621kPa) and the desired output of the voice coil of the valves operating range. should be less than 10lbs (44.5N), these values translate to a diameter of less than 0.35in (0.89 cm) or area of less than 0.1 in2 (0.65 cm2).
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