【单选题】【消耗次数：1】
YB32—200型液压压力机液压系统的特点（ ）
①
系统中使用一个轴向柱塞式高压变量泵供油，系统工作压力由远程调压3调定
②
系统中的顺序阀7调定压力为2．5MPa，从而保证了液压系的卸荷压力不致太低,使控制油路具有一定的工作压力
③
系统中采用了专用的预泄换向阀组8来实现上滑块快速返回前的泄压，保证动作平稳，防止换向时的液压冲击和噪声
④
系统利用管道和油液的弹性变形来保压，方法简单，但对液控单向阀和液压缸等元件密封性能要求较高
⑤
系统中的两个液压缸各有一个安全进行过载保护
⑥
以上说法全正确
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