EXPERIMENTAL MODELS OF ONE WAY VALVES MADE USING RAPID PROTOTYPING

Transcription

1 EXPERIMENTAL MODELS OF ONE WAY VALVES MADE USING RAPID PROTOTYPING Constantin Bucşan, Mihai Avram, Daniel Besnea "Politehnica" University of Bucharest 33 Spl. Independentei, Bucharest Abstract - The paper presents a new approach of designing a pneumatic one way valve: the structure is modular and the basic elements can be combined in order to obtain different types of valves. Functional models of the valves are obtained using Rapid Prototyping technology (FDM Fused Deposition Material) and they are integrated within pneumatic systems in order to test their working performances and to validate the design. Keywords: pneumatic, one way valve, modular design, rapid prototyping, design validation.. Introduction It is well known that the performances of a pneumatic actuating system depend on the performances of each component element within its structure. An analysis of the pneumatic control systems evolution highlights the following trends: - increasing the reliability and accuracy and improving the static and dynamic performances; - reducing the price of the system; - using new types of systems with lower energy consumption; - miniaturizing and modularizing the systems; - integrating the interface electronics within the structure of the system; - using optional interfaces for connecting the actuating system to the data buses; - developing control techniques using modulated pulses for controlling on/off way valves in order to obtain a proportional control of the flow; - using new types of unconventional actuators in the structure of power control devices; - using special fluids in the piloting zone of the proportional devices; - using ecological and biodegradable working fluids; - using environment friendly systems; - extending the concept of "unique supplier"; the producers try to offer a complete range of pneumatic devices, including the control electronics and the connecting elements. The paper deals with a simple pneumatic device - the one way valve and the actions to be taken in order to reduce the costs and to miniaturize and modularize the device. The main steps are the following: - redesigning the pneumatic device; - establishing the machining and assembly technologies.. Pneumatic one way valves Pneumatic one way valves are designed to control the direction of air flow through the circuits on which they are mounted. Some types of one way valves can also perform other functions, such as: dividing and adding the air flows, some elementary logical functions (AND, OR), quick discharge of some circuits. The simple one way valve lets the fluid flow only in one direction and blocks the flow in the opposite direction. A well designed and built one way valve must meet two requirements: - the pressure loss on the flowing direction must be lower than 0,...0, bar; - the closing on the opposite direction must be perfect. The mobile element - the valve - has two steady working positions. From this point of view the device has a discrete functioning. Taking into account that the working fluid is the compressed air, a non-metallic material is needed at the contact zone between the valve and the seat (it is not allowed a metal to metal sealing). There are two ways to solve the problem: inserting non-metallic elements into the metallic valve or making the entire valve of rubber or other materials with good sealing properties, like PTFE. One way valves can be classified, according to the number of orifices, as simple valves (valves with two orifices) and double valves (valves with three orifices). The simple valves are used to control the direction of flow and they can be non-commanded or commanded. The double valves are used to divide the flow, to perform logical functions or to quickly discharge a circuit to atmosphere. Table presents the classification of one way valves along with their symbols. 3

2 Simple valves Table Classification of one way valves Classification Symbol Non-commanded: - without spring - with spring Commanded Non lockable: - pneumatic - mechanic Lockable - pneumatic - mechanic 0 Double valves Circuit divider Circuit selector: - disjunction SAU - conjunction - SI Quick discharger 3 3. Basic elements of the valves structure An analysis of the existing variants of one way valves was performed in order to identify the basic elements of the valve structure that can be combined to obtain any desired structure. Figure show the structure of a simple one way valve, non-commanded, with spring, and figure shows the structure of a lockable one way valve pneumatic commanded. The analysis of the two structures led to the identification of the basic elements of the valves structure: - the valve body, with the machined seat and the two orifices () and (); - the spherical valve, that can also be a flat or conical valve; - the lids and ; - the rod ; - the piston, that can be replaced by a membrane with rigid centre. () 3 () () Figure : Simple one way valve, non-commanded 33

3 3 () () () Figure : Lockable one way valve pneumatic commanded As an example, the basic elements of a Dn valve were designed. Figure 3 shows the obtained results (plus the intermediate part and the push-button ). Figure 3: The basic elements of a Dn valve Different types of one way valves can be obtained by choosing the necessary elements from the designed ones, as follows: - simple valve, non-commanded - figure ; - simple valve, pneumatic or mechanical commanded, non lockable - figure ; - simple valve, pneumatic or mechanical commanded, lockable - figure. () () Figure : Simple valve, non-commanded () () () Figure : Simple valve, pneumatic or mechanical commanded, non lockable () () () Figure : Simple valve, pneumatic or mechanical commanded, non lockable 3

4 . The experimental model The technology of rapid prototyping was chosen to build the experimental model of the valve, due to its advantages: - reduced time and costs; - the possibility to obtain parts with complex shapes; - quick validation of design etc. The 3D model of the valve (figure ) was used to obtain the input data for rapid prototyping printer. Figure shows the parts obtained. Figure : The 3D model of the valve. The testing stand Figure : The component parts of the valve Figure shows the principle scheme of the stand used to test the experimental models of one way commanded, lockable valves. 3

5 MPL S S DP S Figure : The principle scheme of the testing stand The tested valves S and S are mounted on the circuits of the pneumatic linear motor MPL. This way the position of the mobile assembly of the motor along the stroke can be rigorously maintained. The stand is useful for determining the tightness between the parts of the models and also their correct functioning.. Conclusions The modular design of pneumatic systems has certain advantages: lower costs, more flexibility etc. The functional models can be made using Rapid Prototyping technology with reduced time and costs, the possibility to obtain parts with complex shapes and a quick validation of design.. References [] Avram M., Bucsan C., Sisteme de actionare pneumatice inteligente, Editura Politehnica PRESS, Bucuresti, 0; [] Avram, M., Acţionări hidraulice şi pneumatice Echipamente şi sisteme clasice şi mecatronice, Editura Universitară, Bucureşti, 00. 3