In hydraulically operated presses repeatedly the problem is with machinery really maintaining the required pressure and thus the required compression force. The point is obtaining these values and display of a high pressure accuracy during the process.
Basically it cannot be excluded that so called internal leakage, including at hydraulic valves, are caused which may result in a discharge of the hydraulic oil during operation of a machine and thereby will cause pressure losses. This even cannot be excluded completely by using of high quality components. Standard solutions always will react on these internal leakages by starting re-pumping in order to reestablish the required level. The hysteresis until start of this re-pumping in part is considerable.
Moreover some manufacturers use exclusively indicators for the indication of NOMINAL values. This is of course legitimate. However, such indicators only will mask the internal pressure losses if those in fact are not displayed due to the design of an indicator. Properly speaking, a remedy in this case only will be a display of the REAL values by means of a pressure gauge.
Pressure losses – regardless to how much they amount – whether visible or not, even if they are not acknowledged at first sight, always do exist.. However, they can be reduced to a minimum by a well thought hydraulic system. We have taken care of this problem particularly at our laboratory presses in order to reduce such internal pressure losses or compensate them quickly and with small hysteresis by means of an intelligent composition of the components.
System pressure curve:
Example for the real pressure development in a press (e.g. at the LaboPress P200S or P300S or P400S)
The here presented feasible and relatively cheap form of pressure loss compensation (see green “dented curve”) has to be distinguished from the much more elaborate, more expensive but also much more accurate way of keeping the pressure constant by the proportional valve technology. Valves of this type will take care by an electronic control permanently and automatically of the compensation of pressure losses. Also in this field we dispose of corresponding experience, but such a high accuracy will not be required in each case.