Kento Kumagai | Hitachi Construction Machinery Co., Ltd. | Tsuchiura-city, Ibaraki-prefecture | JP
Dr. Ryu Shohei | Hitachi Construction Machinery Co., Ltd. | Tsuchiura-city, Ibaraki-prefecture | JP
Associate Professor. Ph.D. Jun Zou | Zhejiang University | Hangzhou | CN
Professor. Dr. Kazuo Maeno | Chiba University | Chiba-city, Chiba-prefecture | JP
» Details anzeigen
Poppet type valve is one of the most popular components in hydraulics with long history, and widely applied in relief valve, pressure or flow control valve etc. However, since the poppet valve is easy to induce unpredicted vibration of hydraulic system, it is also considered as trouble source in hydraulics. This weakness has also restricted the valve’s application to need delicate pressure or flow controls. Many researchers have devoted to study the problem, and most of them considered it is because of the combined relation of fluid inertia, fluid compressibility, poppet mass, spring, damping, and so on. The consideration is effective for many cases, but it is difficult to clearly explain why same valve may show quite different performance in NEARLY SAME systems, which is also the actual problem for bothered engineers.
Thanks to the advanced experimental visualization technology and digital simulation technology, they make us easy to peer into the inside of the valve, and so we make a renewed study of the old phenomenon. Through the study we found that the vibration of poppet valve does not depend only on the composition of all the parts in valve, but also depends on the cavitation state inside the valve, which is closely influenced by the flow conditions.
The novel experimental system consists of a variable flow rate type piston pump, a convergent flow type poppet valve, which has a visibility valve housing made of acrylic resin, and a throttle valve which is set at the downstream of the poppet valve, and used for adjusting the downstream pressure. The flow rate sensor, pressure sensors at up and down stream of the poppet valve are set and high-speed video camera is used to monitor the flow state and also used as poppet displacement sensor to measure its movement.
A numerical simulation model was built for the same experiment system, the fluid inertia and compressibility are considered in the model, and the model method is referred from typical research.
In experiment, two typical poppet valve cases are studied. CASE1 is to set the damping orifice at 3mm, making the poppet get easy to vibrate, and CASE2 is to set the damping orifice at 1mm, to let the valve not easy to get vibrate.
In both cases, we change the flowrate passing through the valve from 0 to 50L/min, and at every flowrate we change the downstream pressure of the valve from 0 to 1.0MPa, and so to monitor the vibration in valve.
The results show that
1) In CASE1, the poppet would vibrate when the flow is less than 40L/min, and get stable when the flow is over 40L/min. and vibrate frequency is about
550-600Hz for different downstream pressure.
2) In CASE2, as the damping orifice is set from 3mm to 1mm, the valve is
getting steady when flowrate is over 20L/min. Clearly improvement is recognized. However, when the flowrate is less than 20L/min, the vibration will depend on the downstream pressure. When the downstream pressure is below 0.5MPa, and the cavitation bubbles are appeared and along with the decreased pressure, the poppet will get vibrated when the cavitation enhances to some extent.
In simulation, for CASE1, under the conditions of experimental vibration, the simulation also shows the system in vibration state, and the frequency is nearly in same range. For CASE 2, under the condition where the experiment shows no vibration, the simulation also shows no vibration. These results show the simulation has modeled well the essential features of the vibration in this system.
But for CASE2, under the conditions of experimental vibration of the poppet, when the cavitation bobble is increased, the simulation cannot present the vibration state. That means the cavitation is an unpredictable factor of vibration phenomenon.
From this research we found that the cavitation is another reason for poppet valve vibration, and since the quantity of the cavitation is influenced by various flow conditions, that cause’s unpredictable vibration of a valve which may have good repute before.