The design of the hydraulic cylinder test bed based on cartridge valves

Kai-lin FENG, Guan-guo MA, Xiao-xiao GUO,Fu-tao ZUO, Shou-lei JIANG

(Shandong University of Science and Technology, Qingdao 266590, China)



The design of the hydraulic cylinder test bed based on cartridge valves

Kai-lin FENG, Guan-guo MA*, Xiao-xiao GUO,Fu-tao ZUO, Shou-lei JIANG

(Shandong University of Science and Technology, Qingdao 266590, China)

Since the test bed of big hydraulic cylinder needs high pressure and greater flow rate, the hydraulic cylinder test bed based on cartridge valves was designed according to the test standard of hydraulic cylinder and the deficiency of the existing hydraulic cylinder test bed in this paper. It have been proposed that the system of loading hydraulic cylinder and system of test hydraulic cylinder by using the same hydraulic source, so did the system with high pressure and greatflow rate in parallel which could reduce the motors and hydraulic pump. Therefore, the hydraulic cylinder test bed could be obtained which has some characteristics such as higher automation, lower product costing and energy saving.

Hydraulic cylinder test bed, High pressure, Big flow rate, Cartridge valves, Automation

1 Introduction

The hydraulic cylinder is one of the most important components for a hydraulic system. Its quality will affect the performance of hydraulic system directly. With the development of hydraulic technology and strict requirements on the quality of products in china, the test of hydraulic cylinder has become the important way to guarantee the quality. The routine tests and type tests of the hydraulic cylinder test could avoid the hydraulic cylinder below the standard come to the market, which may bring loss to customers.

With the development of automation, more strict demand was put forward for the hydraulic cylinder test bed. We need to guarantee efficiency and reduce manpower, which needs the perfect combination of machine, electric and hydraulic. The hydraulic cylinder test bed has a long history and has a series achievement. But the research to the hydraulic cylinder test bed with high automation, high pressure and greatflow rate is not accomplished so far. So this paper mainly refers to a kind of hydraulic cylinder test bed with high automation, high pressure and great flow rate [1].

2 The design demand of hydraulic cylinder test bed

The hydraulic cylinder test was divided into routine tests and type tests.

Routine tests include:

① Test run；

② The test of the character of start pressure；

③ Pressure-tight test；

④ Leakage test；

⑤ Pumper test；

⑥ Full stroke test [5-6]；

Type tests include：

Type tests not only include the above-mentioned routine tests, but include the load efficiency test, durability test and high-temperature test if it is needed.

This hydraulic cylinder test bed should meet the required demand as follows:

1)It should be able to provide the high pressure of 39.375 MPa, so that it could achieve the pressure-tight test.

2)It should be able to test the hydraulic cylinder with cylinder diameter of Φ80-Φ125 and the stroke of 100-5 000 mm.

3)It should be able to test the hydraulic cylinder with different diameter, different stroke and different installation approach [1].

3 The design of the hydraulic cylinder test bed

During the process of hydraulic cylinder test, high efficiency is needed, which require that the operation speed of the piston of the hydraulic cylinder could reach at least, when the piston runs without loading. And the test bed could test the hydraulic cylinder with the diameter of. Therefore, the flow rate of the test hydraulic pump can be expressed as follows:

(1)

Where,dis the diameter of test hydraulic cylinder.

The highest pressure of the system should meet the requirement of the hydraulic cylinder’s pressure-tight test, which can provide the 1.25 times nominal pressure for the working chamber of the testing hydraulic cylinder. So the pressure that hydraulic pump provides could be evaluated as follows:

p=1.25p0=1.25×31.5=39.375MPa

(2)

Where,pis the greatest pressure that hydraulic pump could provide；p0is the nominal pressure of the system.

But in the actual production, the common hydraulic valves that can support such high pressure as well as such great flow rate is very expensive. Since the leakage of these valves is very strict, a kind of system which could satisfy the high pressure and great flow rate was designed for the hydraulic cylinder test bed, as shown in Fig.1.

In the process of leakage test, the nominal pressure was required to load the test hydraulic cylinder. This hydraulic cylinder test bed adopted the settlement method, in which the loading hydraulic cylinder will exert the pressure to the piston rod of the test hydraulic cylinder and the pressure of the annular seal space of test hydraulic cylinder could reach to the nominal pressure 31.5 MPa.If the displacement of the piston does not catch the setting displacement, the hydraulic cylinder is qualified. Therefore, the flow rate of the loading hydraulic pump could be expressed as follows:

(3)

(4)

Where,F1is the force that the loading hydraulic cylinder applies to the test hydraulic cylinder；A1is the area of the loading hydraulic cylinder piston；p1is the input pressure of the loading hydraulic cylinder，p1=25 MPa；v1is the operation speed of loading hydraulic cylinder’s piston，v1=0.2 m/s；Q1is the flow rate of the loading hydraulic cylinder.

From the equation (4), it could be confirmed that the flow rate of the loading hydraulic cylinder could reach great value and two pumps in parallel are required to supply the hydraulic fluid for this system. The hydraulic system is shown in Fig.1.

Fig.1 The original system of the hydraulic cylinder test bed

Since the system of the loading hydraulic cylinder and the system of the test hydraulic cylinder should have their own directional control valve, the three-position four-way module are designed for these systems based on cartridge valves, as module 5 and module 6 shown in Fig. 1. These modules could not only achieve the three-position four-way the reversing, but also have the same function as safety valve due to the pressure cartridge valves include in these modules.

Of course, in the system of loading hydraulic cylinder and the system of test hydraulic cylinder, the motors can not start and stop under the conditions of hydraulic system, therefore, the hydraulic system is required to have the load-off function. As shown in Fig.1, module 2 and module 3 are the load-off function module which is composed of cartridge valves that could achieve the load-off function and magnetic exchange valve. When the system works, the system could provide hydraulic fluid to hydraulic cylinder when the magnetic exchange valve is supplied with electric energy, and the hydraulic cylinder cannot obtain the hydraulic fluid when the magnetic exchange valve is lack of electric energy, therefore, the system is at unload status.

The module 1 in the system of loading hydraulic cylinder in Fig.1 plays a portion of pressure regulation function, which is consist of a pressure cartridge valve and a proportional relief valve. During the leakage test, the input pressure of the hydraulic cylinder is regulated by adjusting the electric current that is input for the electric magnet of the proportional relief valve, which could change the loading force of hydraulic cylinder applied to the test hydraulic cylinder, so that the pressure of the test hydraulic cylinder could seal the chamber. The regulation of the pressure module 4 in the system of test hydraulic cylinder has the same working principle.

In this hydraulic system of the hydraulic cylinder test bed, some motors and hydraulic pumps are needed, because both the loading hydraulic cylinder system and the test hydraulic cylinder system all need the hydraulic source to support the pressure. Since the loading hydraulic cylinder system and the test hydraulic cylinder system will not work at the same time, one hydraulic source could be used for these two systems and the two-position three-way module and cartridge valves could provide the hydraulic source to support these two systems. The two branch of the hydraulic system could adjust their pressure with the common electromagnetic relief valve 1, and the adjustable hydraulic system is shown in Fig.2.

According to the module 1 in Fig.2, two cartridge valves and two four-way electromagnetic directional valves could be used to make up the two-position three-way module, and the direction of the hydraulic oil could be controlled by using this module. When there is no electric current for the electric magnet 1YA, these hydraulic pumps will provide hydraulic oil to the system of the test hydraulic cylinder, and once the system of loading hydraulic cylinder needs to work, the electric current is given to the electric magnet 1YA through the hydraulic circuit and the system of loading hydraulic cylinder could be adjusted.

Fig.2 The system of the hydraulic cylinder test bed after improvement

In this kind of hydraulic system, the common hydraulic pump could provide pressure to the test hydraulic cylinder and loading hydraulic cylinder, which will save cost. The hydraulic pump should not only provide the high pressure ofp0=39.375 MPa, but also provide the great flow rate ofQ=147.2 L/min. The pump which could meet the requirement is very expensive.

Actually, in the progress of the working of the hydraulic cylinder test bed, such expensive pump used in this hydraulic system is kind of waste, and it will increase the cost and release heat, eventually it will make all the machinery look so heavy. When the test bed works with its maximum flow rate, the output pressure of the hydraulic pump cannot exceed 10 MPa. When the system works at the maximum pressurep0=39.375 MPa, the flow rate of the system is aboutQ0=6 L/min, which is more than the high pressure and the great flow rate cannot come out in this system of the test bed. Therefore, we can realize the high pressure system with small flow rate and low pressure system with relative great flow rate as described in Fig. 3, and it could achieve the required aims and use relative less power.

The motor power in high pressure system with small flow rate in the hydraulic system of the hydraulic cylinder test bed could be described as follows [2]:

N0=pQ0/60η0=

47.25×6/(60×0.95)≈5kW

(5)

The motor power in low system with great flow rate in the hydraulic system of the hydraulic cylinder test bed can be described as follows [2]:

N1=p1Q/60η0=

10×147.2/(60×0.95)=25.82kW

(6)

Where,N1is the power of the motor;p1is the maximum pressure the system could obtain the maximum flow rate.

1.plunger pump; 2.proportional relief module; 3. two-position three-way module; 4,11,13.pressure sensor; 5,12.three-position four-way module; 6.loading hydraulic cylinder; 7.travel switch; 8.force sensor; 9.test hydraulic cylinder; 10.hydraulic compact joint; 14.high pressure hydraulic lock; 15.high pressure selector valve; 16.unloading module; 17.high pressure proportional relief valve; 18.super-pressure pump

Fig.3 The final system of the hydraulic cylinder test bed

As described in Fig.3, when the system needs high pressure, the great flow rate is not needed. At the same time, the electric current could be provided to the electric magnet 2YA, the flow rate in the low pressure system with great flow rate is at the load-off situation. The high pressure oil to these two chambers of the hydraulic cylinder could be changed by on-off of the electric current for the electric magnet 8YA and electric magnet 9YA. Through the current adjustment of the electric magnet 10YA on the high pressure proportional relief valve 17, the pressure in the high pressure system could be changed. When the test hydraulic cylinder needs to run fast, there is no high pressure needed in the test bed system. At the same time, there is no electric current for the electric magnet 8YA and electric magnet 9YA on the high pressure selector valve 15, when the high pressure selector valve is at the middle place, the flow rate of the high pressure system decompresses. There is a high pressure hydraulic lock 14 in the high pressure system, which could ensure the chambers of the test hydraulic cylinder, so that the leakage test could work normally.

4 Conclusions

According to the test standard, a set of hydraulic system that could automatically provide high pressure and relative great flow rate was designed in this paper. The performance of this system was improved, referring to its working situation, in which the two-position three-way valve was used to achieve the arm that the system of loading hydraulic cylinder and the system of test hydraulic cylinder use the same hydraulic source in common. This system could provide the high pressure with small flow rate and the low pressure with relative great flow rate be in parallel, which will greatly reduce the consumed power of the system. Through this system, it could save the power and reduce the heat production. This design method could not only reduce the manufacture costing, but also improve the efficiency. Therefore, it could provide the basis for the later design of hydraulic cylinder test bed.

Acknowledgement

This paper is supported by Postgraduate Innovation Fund of Shandong University of Science and Technology(Grant No.YC140314)

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(Continued on 30 page)

17 September 2014; revised 26 March 2015;

Guan-guo MA, E-mail:156154682@qq.com

10.3969/j.issn.1001-3881.2015.18.004 Document code: A

TH137.51

accepted 9 May 2015

Kai-lin Feng, Professor. E-mail:156154682@qq.com

Hydromechatronics Engineering

http://jdy.qks.cqut.edu.cn

E-mail: jdygcyw@126.com