今天看到公司O的一步咖啡机，其中又说到这台咖啡机可以有调节OPV的功能，那究竟什么是OPV呢？
opv其实就是over pressure valve 过压保护阀。其作用就是在咖啡机器中，让咖啡酿造的压力不至于太高，一般设定在10bar以内，也就是说，单使用的咖啡粉过细的时候，这时候管路中的OPV就发挥作用，过压的水从OPV 支路上泄露出去。
特别是用震动泵的时候，因为内部压力是呈现间隙性忽高忽低的情况，其实就是一条波浪线一样的压力曲线，而使用OPV之后就可以消减部分波峰的压力，从而让咖啡整体萃取的压力控制在10bar 以内。
那为什么要9bar的压力呢，是因为超过10bar ，咖啡萃取就会过度，萃取的咖啡就会发苦，把一些不好的物质给萃取出来，自然味道就没这么好了。
OPV does not set the brewing pressure | Contrary to popular belief the OPV does not set the brewing pressure or pump pressure of the espresso machine, it is impossible to set the machine to extract at a certain pressure. What the OPV does is to set an "upper limit" to the brewing pressure by limiting the pressure applied to the brewing system by the pump, with excess pump pressure (or flow) being either returned to the pump inlet or water tank depending on the type of pump.
OPV不设定冲泡压力|与人们普遍认为的OPV不设定浓缩咖啡机的冲泡压力或泵压力相反，不可能设定机器在一定压力下提取。OPV的作用是通过限制泵对酿造系统施加的压力来设置酿造压力的“上限”，根据泵的类型，超过的泵压力(或流量)要么返回到泵入口或水箱
OPV is typically set to 9-10 bar | it is generally excepted that the optimum espresso extraction is achieved at 9-10 bar of pressure. Above this pressure, undesirable flavours tend to be forced out of the ground coffee and into the drink, this is commonly known as over-extraction. If your espresso machine has an extraction pressure gauge then when brewing coffee the pressure should indicate 9-10 bar of pressure. When backflushing your machine, you would expect the extraction pressure to be about 1 bar higher than during a normal extraction.
OPV通常设置为9-10 bar;通常情况下，最佳的浓缩咖啡提取是在9-10 bar的压力下实现的。超过这个压力，不受欢迎的味道往往会从咖啡粉中挤出来，进入饮料中，这通常被称为过度萃取。如果你的浓缩咖啡机有萃取压力表，那么当冲泡咖啡时，压力应该显示9-10巴的压力。当对机器进行反冲洗时，您可能期望提取压力比正常提取时高出约1巴。
Extraction pressure is still set by the barista | the extraction pressure is still determined by the grind, dose and tamp of the coffee. Too course a grind, too little ground coffee, or insufficient compression of the coffee will cause the
萃取压力仍然由咖啡师设定，萃取压力仍然由咖啡的研磨、剂量和压实来决定。太多的研磨，太少的咖啡粉，或咖啡压缩不足都会导致
OPVs are are found in both commercial and high-end domestic espresso machines. In commercial espresso machines fitted with the most common Procon or Fluid-o-Tech pumps the OPV is typically incorporated into the pump between the inlet and the outlet. The OPV can be adjusted to set the pressure at the outlet with the excess water being distributed back to the inlet.
opv在商用和高端的家用浓缩咖啡机上都可以找到。在配备最常见的普康或Fluid-o-Tech泵的商用浓缩咖啡机中，OPV通常被整合到泵的入口和出口之间。可以调节OPV以设置出口压力，多余的水被分配回进口。
On espresso machines that use vibration pumps; tylically domestics espresso machines; the OPV is a separate component usually located just after the outlet of the pump. In this configuration the OPV can be adjusted to set the pressure at the outlet with the excess water being distributed out of a return. This return is typically connected to a silicon sube that runs back into the water reservoir (this is what the second water reservoir tube is for).
在使用振动泵的浓缩咖啡机上;通常是家用浓缩咖啡机;OPV是一个独立的组件，通常位于泵的出口之后。在这种配置中，可以调整OPV以设置出口压力，多余的水从回流中分配出去。这个返回通常连接到一个硅管，运行回水库(这是第二个水库管是什么)。
