Pneumatic Valve's Seal Dynamic Load - Science Direct

2 downloads 0 Views 739KB Size Report
Keywords:Dynamic loading; sealing element; valve pair; pneumatic actuator. .... 6 - unit boundary conditions; 7 - information-measuring system; 8 - the hydraulic ...
Available online at www.sciencedirect.com

ScienceDirect Procedia Engineering 176 (2017) 699 – 705

Dynamics and Vibroacoustics of Machines

Pneumatic Valve’s SealDynamic Load Salimzhan A. Gafurova,b*, Vera A. Salminaa, Yuri I. Kondrashova a

Samara National Research University, Samara, Russian Federation b Lappeenranta University of Technology, Lappeenranta, Finland

Abstract This article presents the experimental study of the pneumatic valve’s dynamic loading. The influence of structural and technological factors on the stress state of the sealing elements and their tightness are estimated. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility ofthe organizing committee of the international conference on Dynamics and Vibroacoustics of (http://creativecommons.org/licenses/by-nc-nd/4.0/). Machines. under responsibility of the organizing committee of the international conference on Dynamics and Vibroacoustics of Machines Peer-review Keywords:Dynamic loading; sealing element; valve pair; pneumatic actuator.

1. Introduction

Nomenclature Py1, Py2 PP PBL P2 T FOUT PNOM V0

pressure in the control chamber, MPa work pressure, MPa blowing pressure, MPa hydrotesting pressure, MPa temperature, K external vibration disturbance, kg/s nominal pressure, MPa initial speed, m/s

__________ * Corresponding author. Tel.: +7-927-715-0001; E-mail address: [email protected]

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the international conference on Dynamics and Vibroacoustics of Machines

doi:10.1016/j.proeng.2017.02.315

700

Salimzhan A. Gafurov et al. / Procedia Engineering 176 (2017) 699 – 705

Nowadays there are a number ofvalves designs. They are thoroughly discussed in papers [5, 6].There are a number of requirements for pneumatic valves such as fast-responding, impermeability as pneumatic valves largely determine the reliability of the whole mechanical system [1]. Conducted literature overview showed a number ofpapers devoted to valves reliability. They mostly focus on valve’s sealing elements. Paper [2] shows the investigation of pneumatic aggregates failures and their reasons. The main conclusion of this work is that the main reasons of pneumatic valves failures are seals. Approximately 34 % of the total number of failures were caused by seals damages. Valve seals performances are known to be mainly determined by behaviorof stress and deformations distributions over time. Paper [3] shows that valve units experience significant dynamic loadsduring operation. Paper [3] also describes the main reasons of dynamic loading of investigated valves. Paper [4] also proves that the main elements that determine the lifetime and reliability of valves are sealing elements. Paper [7] notices that extremely high dynamic loads occur in seals in case of cyclic changes in a wide range of environment temperature as well as in case of influence of external overloads. Such dynamic loads lead to loss of impermeability. Main sources of external overloads are considered in paper [8]. Theoretical and experimental methods are widely used forinvestigation of valves dynamic loading.A theoretical model for study of pneumatic sealing elements loading state was proposed in paper [9]. This work indicates that the maximum dynamic load,occurring in case of collision of valves elements, at least in 2 times higher than static load. Therefore, limit value of the dynamic coefficient, used in calculations to avoid a rebound, should be significantly increased by introducing structural damping. The state-of-the-art of methods forvalve working processes calculation as well as principles for design the unloaded pneumatic valves with variable external load are described in paper [10]. Paper [11] formulates the design and technological recommendations for controlled valves developing. However, a variety of structural, technological and operational factors influence on the operation of the valve seals of pneumatic valves. The complexity of the analytical description of these influences requires experimental investigations for studying valveloading state. Additionally, existing theoretical methods and approaches require a significant amount of experimental data about the parameters of the fluid system’s working process. In fact,valve actuation leads to a number of phenomena that complicate mathematical calculations as they influence on the working processes in valves’ seals: design features of the actuating drive, energy losses due to friction, vibration loading, depending on the valve installation location in the system and others. Usually, the following assumptions are made in theoretical simulations: 1. Heat exchangewith the environment is neglected. 2. Internal and external leakage of compressed gasare neglected. 3. Temperature of the compressed gas in the control chambers of the pneumatic system is assumed to be constant as the valve operates very short time. 4. Parameters distribution of a pneumatic system as well as local resistances are not taken into account. 5. Neglect the force of viscous friction during the deformation seal of the valve seal. Such assumptions significantly reduce the accuracy of theoretical simulations. Therefore, to estimate the dynamic loading state of the valve seal, besides the seal, the whole pneumatic aggregate should be considered. Therefore,experiments are needed to investigate the dynamic loading state of the valve as theoretical data is not enough to do it. 2. Test object and bench This paper presents the experimental results of the investigation of aviation valve loading state. Considered valve is presented in Figure 1. The valve represents the class of spring valves. It works with air drives both unilateral and bilateral actions. Due to the small volume of chambers of the pneumatic actuator, the valve provides a wide range of impact velocityof sealing elements. This is a reason why such valve was chosen for dynamic tests.Technical characteristics of the valve are shown in Table 1.

Salimzhan A. Gafurov et al. / Procedia Engineering 176 (2017) 699 – 705

Fig. 1 Test object. 1 – cover; 2 – body; 3 – upper plate spring; 4 – upper plate; 5 – lower plate spring; 6 – lower plate; 7 – body; 8 – nozzle. Table 1. Object’s characteristics Characteristics

Value

Power pressure

Up to 50 MPa

Control pressure

Up to 15 MPa

Nominal diameter of flow cross sectionsof removable sealing elements

10…32 mm

Pneumatic piston-stroke

8.5 mm

Maximum impact velocity of sealing elements

4 m/s

Investigations were carried out on three valve typical operation modes for the experimental determination of its dynamic loading that occur in the valve: 1. Seal's valve plate moves due to control force and resistance forces. 2. Seal closing is accompanied by impact processes (rebounds may be observed). 3. External disturbances influence on the valve seal on the stationary operating modes. These disturbancesare transmitted through the mounting of the unit, operation and control environment. Such choice of operating modes has been made due to the fact, that elements of the valve seal - plate and saddle, come into contact due to valve operation. This impact leads to additional dynamic loads. Thus, such interaction is accompanied by external disturbances generated by the operation environment.Developed experimental system for investigations of dynamic loading state of the considered valve is shown in Figure 2.

701

702

Salimzhan A. Gafurov et al. / Procedia Engineering 176 (2017) 699 – 705

Fig. 2 Block diagram and photo of the experimental test bench:1 - compressor; 2 - filter; 3 - receiver; 4 - distribution control valves; 5 - test valve; 6 - unit boundary conditions; 7 - information-measuring system; 8 - the hydraulic pump; 9 - shaker; 10 – cryostat

According to the diagram shown in Figure 2, the input parameters for the investigation were the pressure in the control chambersРУ1, РУ2, working pressure РР, blowing pressure РBL, proof-test-pressureР2, the temperature T and external vibration disturbance FOUT.Parameters, РУ1, РУ2, РР, РBLareprovided by a compressor 1, an air filter 2, receivers 3 and distribution control valves 4. If necessary, low temperatures are supported the refrigeration chamber or cryostat 10. External perturbations are defined by a vibration table 9. Proof-test pressure is carried out by a pump 8before testing. The block of aggregates, 6,simulating the environment by boundary conditions provides the required conditions of units mounting, the type of supply lines, damping, etc. Parameters of impact interaction of seals elements, such as speed of moving parts before collision, contact force, elements vibration are defined by measurement system 7. This system controls inputs parameters that may vary or be maintained at a certain level due to the presence of feedback. The structural circuit of the test bench is shown in Figure 3.The object of study, depending on the type of problem is being solved, is mounted directly on the control panel and placed in a cryostat, fixed to the vibration table or vibration isolated base.Main technical characteristics of the experimental setup is shown in Table 2.

Fig. 3 Structural circuit: 1 - compressor station; 2 - high pressure receivers; 3 - distribution panel; 4 - the object of study; 5 - remote control Table 2. Test Bench Characteristics Characteristics

Value

Power pressure (air)

Up to 40 MPa

Control pressure (air)

Up to 20 MPa

Maximum flow rate

Up to 10 kg/s

Proof-test pressure

Up to 40MPa

3. Experimental investigations Fluid control pressure, contact force, displacement of the drive shaft, the convergence of seal elements and valve case vibration were sampled and processing. Mean value of the loading force as well as loading velocity were constant over tests.

Salimzhan A. Gafurov et al. / Procedia Engineering 176 (2017) 699 – 705

Loading of the seal wasapplied consequently without reassembling in order to avoid the variation of mechanical properties of the seal material. During tests the rest of materials was supposed. Loading level was varied in a range of (0.5 ... 1.5)РNOM. Figures 4 a and b shows obtained experimental dependences between the control pressure and the amount of displacement of the valve stem, and the speed of its displacement correspondingly.

Fig. 4 Variation of the controlpressure for the valve trim

Figure 4b shows that the area of the hysteresis loop increases more than in 2 times due to increasing of displacement velocity from 0.001 m/s to 0.52 m/s (Fig. 4b, curves 1 and 4). This indicates that the energy dissipation in the piston ring seals drive play an important role not only inertial forces and dry friction and viscous component. The dynamic characteristics of the valve unit were estimated by means of frequency analysis of transient processes occurring at the valve closing operating regimes. The obtained results are shown in Figure 5.

Fig. 5 Transient regimes at average speed: a) 0.12 m/s; b) 0.3 m/s; c) 0.4 m/s.

Obtained results allow us to estimate the initial velocity of the valve plate collision with the saddle. Figure 5a shows that control pressure from the chamber under the pistondecreases exponentially with a small area under the curve at the closing operating regime. Figures 5b and 5c present the bigger pieces of transientprocesses, where the area corresponding to the closing operating regime is highlighted. The initial stage of the operation is accompanied by the acceleration of the piston. Further section of the curve is close to a straight line up the impact of the valve elements. Such behaviour of the curve allows you to unambiguously identify the initial speed V0 of the plates and saddles impact. The initial impact velocity of valve plate rebounding from the saddle, may be obtained by analysing the body vibro-record at different average speeds of plate contact with the saddle. Vibro-records of corresponding transient

703

704

Salimzhan A. Gafurov et al. / Procedia Engineering 176 (2017) 699 – 705

regimes which are show in Figure 5, are represented in Figure 6. The transition process in Figure 5a corresponds to vibro-recordin Fig. 6a. Figure 6b corresponds to Figure 5b, figure 5c - to 6c.

Fig. 6 Vibration acceleration vs stroke velocity: a) V0 = 0.16 m / s; b) V0 = 0.5 m / s; a) V0 = 0.8 m / s.

Analysis of the valve case vibro-record at different average speeds of valve plate landing on the saddle, and the dependence of peak acceleration to the body plate from the initial impact velocity, allow us to determine the value of the initial impact velocity V0, at which the valve seat from the rebound. There is one rebound at impact velocities V0= 0.1-0.15 m/s, two – atvelocitiesmore than 0.15 m/s, and three – velocities more than 0.5 m/s. In the valve seals, instantaneous stiffness is only nonlinear parameter. The deviations from the desired geometry and errors of valve contacting elements locations are significantly effect on the behaviour of valve elements rapprochement. In addition, thermal deformations of valve elements effect on elastic component of resistance. Therefore, construction solutions for reducing velocities of plate landing on the seat should be considered to increase the resource of pneumatic actuator. This velocity determines the nature and magnitude of valves dynamic loading. Moreover, viscous forces besides the inertial forces and dry friction should be considered for estimation the power dissipation in the drive 4. Conclusion The paper presents experimental data for the valve seal dynamic loading investigation. Obtained results shows that rebounds occur even at low speed of valve pale and seat impact (0.1 ... 0.2 m/s). Increasing of the impact speed leads to decreasing of the influence of the nonlinear force, occurring due to the valve elements contact, on the evolution of the impact process. Approximately 70% of the whole distance, valve seal moves with a constant speed. Then its velocity slows down. It is caused by the exponential decreasing law of the control movement. High rigidity of the seal absorbs a significant part of the energy and converts it into the deformation. So, there are no conditions for the acceleration of the valve plate due to the direct proportion between its displacement and control pressure. This fact does not allow to vary velocity of valve plate in a wide range. Experiments has shown that rebounds can occur in such construction only at high velocities of valve plate displacement (more than 0.3 m/s). Investigation of the load cycles effect on the characteristics of the seal has shown that the viscous component of resistance reduces insignificantly (less than 5%) after 100…1000 cycles of operation. The accumulation of irreversible deformations for 1000 operation cycles and at the load equal to P = 1.5РNOM in average is 20 microns. At that, the load keeps constant for a while and then valve have a rest for 5 minutes.Thus, provided investigations described the deformation process of valve seal and showed that its characteristics depended on the individual properties of the sample and the operating temperature. Acknowledgements This work was supported by the Ministry of Education and Science of the Russian Federation in the framework of the implementation of the Program ‘‘Research and development on priority directions of scientific-technological complex of Russia for 2014– 2020.

Salimzhan A. Gafurov et al. / Procedia Engineering 176 (2017) 699 – 705

References [1]

Craig Warren Gustafson, The Fluid Mechanics of Hydraulic Fracturing, University of Illinois at UrbanaChampaign, 1987, pp. 322; [2] Chengjiun He, Lili Wang, Jianlin Yan, Qinglin Ma, Environment Controls System Fault Diagnosis Expert System, Proceedings of the First Symposium on Aviation Maintenance and Management – Volume I, Volume 296 of the series Lecture Notes in Electrical Engineering, 2014, pp453-462; [3] Peter Lauer, Advanced Proportional Servo Valve Control with Customized Control Code using White Space. In: The 10th International Fluid Power Conference (10. IFK). Dresden, 2016, pp.137-144; [4] Yu J., Jiao Z., Wu S., Design and simulation study on new servo valve direct driven by piezoelectric actuator using hydraulic amplification, Journal of Mechanical Engineering, V.49, pp 151-158; [5] A. Parr, Hydraulics and Pneumatics. A Technician’s and Engineer’s Guide, Elsevier Ltd, 2011, pp. 233; [6] Chris Stacey, Practical Pneumatics, Routledge, Ltd, 2012; pp. 208; [7] Jaihai Huang, Long Quan, Youshan Gao, Characteristics of Proportional Flow Control Poppet Valve with Pilot Pressure Compensation, In: The 10th International Fluid Power Conference (10. IFK). Dresden, 2016, pp.157-168; [8] Bernard Zahe, Peter Robson, Selection of Load Holding Valves with Lowest Possible Power Losses. In: The 7th International Fluid Power Conference (7. IFK). Aachen, 2010, pp.87-98; [9] S.V. Gerasimov, A.M. Dolotov, U.I. Belogolov, Matematicheskaya model dinamicheskogonagruzheniyauplotneniya s obolochechnumelementom (Mathematical model of dynamic loading of the seal with the shell elements); T:2, 2012, pp. 121-125; (in Russian) [10] PatrikBordovsky, Katharina Shmitz, Hubertus Murrenhoff, CFD Simulation and Measurement of Flow Forces Acting on a Spool Valve. In: The 10th International Fluid Power Conference (10. IFK). Dresden, 2016, pp.473-484 [11] Christoph Boes, Actual Trends in the Design and Development of Valves and Actuator Control. In: The 8th International Fluid Power Conference (8. IFK). Dresden, 2012, pp.437-450.

705