液壓元件逐步實現了標準化、系列化，其規格、品種、質量、效能都有了很大提高，尤其是採用電子技術、伺服技術等新技術新工藝後，液壓系統的質量得到了顯著的提高，其在國民經濟及軍事工業中發揮了重大作用。從不同的角度出發，可以把液壓系統分成不同的形式。 1）按油液的迴圈方式，液壓系統可分為開式系統和閉式系統。開式系統是指液壓泵從油箱吸油，油經各種控制閥後，驅動液壓執行元件，回油再經過換向閥回油箱。這種系統結構較為簡單，可以發揮油箱的散熱、沉澱雜質作用，但因油液常與空氣接觸，使空氣易於滲入系統，導致機構運動不平穩等後果。開式系統油箱大，油泵自吸效能好。閉式系統中，液壓泵的進油管直接與執行元件的回油管相連，工作液體在系統的管路中進行封閉迴圈。其結構緊湊，與空氣接觸機會少，空氣不易滲入系統，故傳動較平穩。工作機構的變速和換向靠調節泵或馬達的變數機構實現，避免了開式系統換向過程中所出現的液壓衝擊和能量損失。但閉式系統較開式系統複雜，因無油箱，油液的散熱和過濾條件較差。為補償系統中的洩漏，通常需要一個小流量的補油泵和油箱。由於單杆雙作用油缸大小腔流量不等，在工作過程中會使功率利用下降，所以閉式系統中的執行元件一般為液壓馬達。 2）按系統中液壓泵的數目，可分為單泵系統，雙泵系統和多泵系統。 3）按所用液壓泵形式的不同，可分為定量泵系統和變數泵系統。變數泵的優點是在調節範圍之內，可以充分利用發動機的功率，但其結構和製造工藝複雜，成本高，可分為手動變數、儘可能控變數、伺服變數、壓力補償變數、恆壓變數、液壓變數等多種方式。 4）按向執行元件供油方式的不同，可分為串聯絡統和並聯系統。串聯絡統中，上一個執行元件的回油即為下一個執行元件的進油，每通過一個執行元件壓力就要降低一次。在串聯絡統中，當主泵向多路閥控制的各執行元件供油時，只要液壓泵的出口壓力足夠，便可以實現各執行元件的運動的'複合。但由於執行元件的壓力是疊加的，所以克服外載能力將隨執行元件數量的增加而降低。並聯系統中，當一臺液壓泵向一組執行元件供油時，進入各執行元件的流量只是液壓泵輸出流量的一部分。流量的分配隨各件上外載荷的不同而變化，首先進入外載荷較小的執行元件，只有當各執行元件上外載荷相等時，才能實現同時動作。 全液壓傳動機械效能的優劣，主要取決於液壓系統性能的好壞，包括所用元件質量優劣，基本回路是否恰當等。系統性能的好壞，除滿足使用功能要求外，應從液壓系統的效率、功率利用、調速範圍和微調特性、振動和噪聲以及系統的安裝和除錯是否方便可靠等方面進行。 現代工程機械幾乎都採用了液壓系統，並且與電子系統、計算機控制技術結合，成為現代工程機械的重要組成部分。
The hydraulic presses system of the form and the evaluation
The hydraulic presses the component to carried out to standardize gradually, the series turn, its specification, species, quantity, functionses all had to raise very greatly, particularly is to adopt the new craft of new technique of electronics technique, servo . after, the hydraulic presses the exaltation that the quantity of the system gets to show the highest , it developped the important function in national economy and the military industries.
Set out from the different angle, can press the system to the liquid to be divided into the different form.
1）Press the circulating way of the oil liquid, the liquid press the system and can is divided into the open type system and shut type open type system mean that the liquid presses the pump to absorb the oil from the fuel tank, the oil is through various control valve, driving the liquid to press to carry out the component, returning to oil to has been changed to return to fuel tank toward valve kind of system structure is more simple, can develop the fuel tank to spread hot, precipitate the miscellaneous quality function, but often get in touch with with air because of the oil liquid, make air be easy to seep into the system, causing the organization exercise the gravamen steady etc. open type system fuel tank is big, oil pump from absorb the function and the shut type system, the liquid presses the pump of into pipeline directly with performance the component return to pipeline connect with each other, work the liquid carries on closing the circulation in the tube road of the structure tightly packed, with the air opportunity to get in touch with little, not easy infiltration system of air, so spread to move more work organization become soon and change to depend to regulate the pump or motors to change to measure the organization realization, avoided the open type system change toward process appear of liquid press the impact and energy the shut type system more the open type system complications, because of having no fuel tank, the oil liquid spread hot and filter the condition is order to compensate the leakiness in the system, usually need a small discharge to repair the oil pump and fuel use the oil a size of a function of high bar discharge not etc., will make power make use of descend in work process, so the performance component within the shut type system presses the motor for the liquid generally.
2）According to system the liquid presses the number of the pump, can is divided into the list pump system, double pump system and pump system more.
3）Press the dissimilarity of pump the form with the liquid by, can is divided into the fixed amount pump system and change the quantity pump advantage that changes to measure the pump is to regulate the scope inside, can make use of the power of launch the machine well, but its structure and the manufacturing craft complications, the cost is high, can is divided in to move to change the quantity, control to change the quantity possibly, servo change the quantity, pressure to compensate to change the quantity, press to change the quantity, liquid to press to change to measure various ways of etc..
4)Press toward performance the component to provide the dissimilarity of the oil method, can is divided in to establish the system and merge the blish in the system, it is next performance component that previous performance component return to oil of into oil, pass a performance component pressure and will lower once each establish system, the each performance component that be the lord pump toward many roads valve control provides the oil, as long as the liquid presses the exit pressure of the pump enough, the compound of the sport that can carry out each performance component the pressure of the performance component is to fold to add of, so overcome the outside carry ability will with carry out the increment of the component quantity but e in the system, be a the pedestal liquid to press the pump toward a performance component to provide the oil, discharge that enters each performance component be just the liquid press the pump exportation discharge of a allotment of the discharge with each last the outside carries the lotus of dissimilarity but variety, enter first outside carry the smaller performance component of lotus, only be each performance component up outside carry the lotus equality, then can carry out to act at the same time.
The whole liquid presses to spread the good and bad of move the machine function, mainly being decided by the quality that the liquid presses the system function, including the component quantity good and bad use, basic back track whether fitting quality of the system function, in addition to satisfying to use the function to request, should make use of, adjust from the efficiency, power that the liquid press the system soon scope and tiny adjust characteristic, vibration and voice of noises and the gearing of the systems and adjust to try whether convenient credibility etc. carry on.
The modern engineering machine almost adopts the liquid to press the system, and combine with electronics system, the calculator control technique, the importance that become the modern engineering machine constitutes the part.