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Which one of circuit is better ?

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tendem

Mechanical
Joined
Nov 12, 2010
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Good day Sir
Because, in my town, it is very very difficult to buy the directional control valve accordance with design. So i usually the other type (not proper) to replace for the proper valve. So please help me to compare 2 circuit with the same function,THE SECOND VALVE is use to combine flow on the left pump to the right pump. (I am not draw the relief valve, filter..).All of valve in the circuit are two stage valve.
 
In the first circuit, I will block the port B, when combine pumps, I just supply the pilot pressure for the left position ( I must do this because I can not buy the valve 3 way, 2 position).if there is leakage at port P when the valve is in neutral,little delivery with go to tank by port T of second valve , so the pressure in the motor 2 and 3 cannot be hight, because there is loss of pressure at port P of valve 2.
In the second circuit, I use 4/3 valve as 4/2 valve, spring offset, When I need combine left pump for right pump, I supply the pilot pressure for Valve is in the center position. Because someone say that , due to construction, port T of lower stage of two stage valve cannot suffer the hight pressure, eventhought Ports T of the lower and upper stage is sepparate (is it right?) (I can not buy the valve that port P,A,B connect together) I am afraid the the seccond circuit work not proper at the hight pressure (250 bar)
- So please help me to compare which circuits is the better ?
- The second motor use to lift the boom of the crawler crane without the counterbalance valve .is it safe?
- The circuit can be work proper ?
Thank you very much
 
 http://files.engineering.com/getfile.aspx?folder=de26edb4-8403-4c6e-b7bb-5f493180c9ad&file=ScreenHunter_03_Sep._29_07.28.jpg
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