相通，作用在變量大柱塞左端面上，這樣變量大、小柱塞上都作用著與出口壓力基本相同的壓力油，而A::Az=2: 1,面積大的油壓力大，因而定子5被推向右邊，定子和轉(zhuǎn)子處于最大偏心距emax的位置，泵輸出最大流量;而當泵出口壓力(系統(tǒng)壓力)達到恒壓閥的調(diào)定壓力值時，如液壓系統(tǒng)需要的流量等于泵的最大流量，則閥芯3維持原位不動;當系統(tǒng)所需流量小于泵提供的流量時，系統(tǒng)壓力便會因流量供過于求而升高，這樣閥芯3下移，使B和T部分溝通，大柱塞左腔的壓力便降下來，而變量小柱塞右端仍暫為高壓油，于是大、小柱塞受力不平衡，定子5左移，而使偏心距減小，泵輸出流量也隨之減少，直至泵提供的流量與系統(tǒng)所需的流量相匹配，泵出口壓力又恢復到彈簧2調(diào)定的壓力值，閥芯3又回到中間位置，這樣便恒定了泵的出口壓力，稱為“恒壓泵”。由于控制口為負遮蓋，要消耗部分控制流量回油箱，但控制性能較好。

      圖8-9(b)為先導式恒壓閥控制的恒壓變量葉片泵，與圖(a)的直控式相比，工作原理相同，其區(qū)別與傳統(tǒng)壓力閥中的直動式和先導式三通減壓閥的區(qū)別類似。與泵出口壓力相比較的不再是彈簧力，而是固定液阻和可調(diào)壓力閥的閥口構(gòu)成B型半橋的輸出壓力，彈簧只起復位作用。另外， 先導式可以進行遙控和選擇多種輸人方式:如手動、機動及比例控制等。
常規(guī)型號：
德國力士樂柱塞泵A10VSO 10排量：
A10VSO10DR/52R-PPA12N00
A10VSO10DR/52L-PKC64N00
A10VSO10DR/52L-PPA14N00
A10VSO10DR/52L-PUC64N00
A10VSO10DR/52L-PUC64N00E
A10VSO10DR/52R-PKC14N00
A10VSO10DR/52R-PKC64N00
A10VSO10DR/52R-PKC64N00E
A10VSO10DR/52R-PKC64N00 ESO857
A10VSO10DR/52R-PKC64N00 ESO858
A10VSO10DR/52R-PKC64N00 ESO938
A10VSO10DR/52R-PKC64N00 ESO938
A10VSO10DR/52R-PKC64N00-SO857
A10VSO10DR/52R-PKC64N00-SO858
A10VSO10DR/52R-PKC64N00-SO938
A10VSO10DR/52R-PPA14N00
A10VSO10DR/52R-PPA14N00E
A10VSO10DR/52R-PPA14N00-SO846
A10VSO10DR/52R-PPA14N00-SO857
A10VSO10DR/52R-PPA14N00-SO858
A10VSO10DR/52R-PPA64N00
A10VSO10DR/52R-PSA14N00
A10VSO10DFR/52L-PKC64N00
A10VSO10DFR/52L-PKC64N00 E
A10VSO10DFR/52L-PUC64N00
A10VSO10DFR/52R-PKC14N00
A10VSO10DFR/52R-PKC64N00
A10VSO10DFR/52R-PKC64N00 E
A10VSO10DFR/52R-PKC64N00-S1645
A10VSO10DFR/52R-PPA14N00
A10VSO10DFR/52R-PPA14N00-SO858
A10VSO10DFR/52R-PSA14N00-SO858
A10VSO10DFR/52R-PSC64N00
A10VSO10DFR/52R-PUC64N00
A10VSO10DFR/52R-PUC64N00 E
A10VSO10DFR/52R-PUC64N00 E
A10VSO10DFR/52R-PUC64N00 ESO857
A10VSO10DFR/52R-PUC64N00-SO857
A10VSO10DFR/52R-VUC14N00
A10VSO10DFR/52R-VUC14N00-SO420
A10VSO10DFR1/52L-PKC64N00
A10VSO10DFR1/52L-PPA14N00
A10VSO10DFR1/52L-PSC14N00
A10VSO10DFR1/52L-PSC64N00
A10VSO10DFR1/52L-PUC64N00
A10VSO10DFR1/52R-PKC64N00
A10VSO10DFR1/52R-PKC64N00 E
A10VSO10DFR1/52R-PKC64N00 E
A10VSO10DFR1/52R-PKC64N00-SO857
A10VSO10DFR1/52R-PKC64N00-SO858
A10VSO10DFR1/52R-PPA14N00
A10VSO10DFR1/52R-PPA14N00-S1482
A10VSO10DFR1/52R-PPA14N00-SO857
A10VSO10DFR1/52R-PPA14N00-SO858
A10VSO10DFR1/52R-PSA14N00-S1915
A10VSO10DFR1/52R-PSA14N00-SO32
A10VSO10DFR1/52R-PSC14N00
A10VSO10DFR1/52R-PSC14N00-SO32
A10VSO10DFR1/52R-PSC64N00
A10VSO10DFR1/52R-PSC64N00E
A10VSO10DFR1/52R-PSC64N00 ES1768
A10VSO10DFR1/52R-PSC64N00-S1768
A10VSO10DFR1/52R-PUC64N00
A10VSO10DFR1/52R-PUC64N00E
A10VSO10DFR1/52R-PUC64N00E
A10VSO10DFR1/52R-PUC64N00-SO857
A10VSO10DFR1/52R-VPA14N00
A10VSO10DFR1/52R-VUC64N00
A10VSO10DR/52R-PSA14N00-S1482
A10VSO10DR/52R-PSA14N00-SO32
A10VSO10DR/52R-PSA14N00-SO857
A10VSO10DR/52R-PSC64N00
A10VSO10DR/52R-PSC64N00E
A10VSO10DR/52R-PSC64N00-SO858
A10VSO10DR/52R-PSC64N00-SO922
A10VSO10DR/52R-PUC14N00
A10VSO10DR/52R-PUC14N00
A10VSO10DR/52R-PUC64N00
A10VSO10DR/52R-PUC64N00E
A10VSO10DR/52R-PUC64N00-S1768
A10VSO10DR/52R-PUC64N00-SO857
A10VSO10DR/52R-PUC64N00-SO858
A10VSO10DR/52R-VKC64N00 ES1768
A10VSO10DR/52R-VKC64N00-S1768
A10VSO10DR/52R-VPA14N00
A10VSO10DR/52R-VPA14N00-SO857
A10VSO10DR/52R-VSC64N00-SO857
A10VSO10DRG/52L-PSC64N00
A10VSO10DRG/52L-PUC64N00
A10VSO10DRG/52R-PKC14N00
A10VSO10DRG/52R-PKC64N00
A10VSO10DRG/52R-PKC64N00 E
A10VSO10DRG/52R-PKC64N00-SO846
A10VSO10DRG/52R-PKC64N00-SO857
A10VSO10DRG/52R-PKC64N00-SO858
A10VSO10DRG/52R-PPA14N00
A10VSO10DRG/52R-PPA14N00-SO857
A10VSO10DRG/52R-PPA14N00-SO858
A10VSO10DRG/52R-PPC14N00
A10VSO10DRG/52R-PSC14N00
A10VSO10DRG/52R-PSC14N00-SO857
A10VSO10DRG/52R-PSC64N00
A10VSO10DRG/52R-PUC14N00
A10VSO10DRG/52R-PUC64N00
A10VSO10DRG/52R-PUC64N00-SO857 

A10VSO 18排量：
A10VSO18DR/31R-PPA12N00
A10VSO18DR/31R-PPA12K01
A10VSO18DFR1/31R-PPA12N00
A10VSO18DFR1/31R-PPA12N00
A10VSO18DFR1/31R-PPA12K01
A10VSO18DFR/31R-PPA12N00
A10VSO18DFLR/31R-PPA12N00
A10VSO18DG/31R-PPA12N00
A10VSO18DRG/31R-PPA12N00
A10VSO18DFE1/31R-PPA12N00
A10VSO18FHD/31R-PPA12N00
A10VSO18ED/31R-PPA12N00

德國力士樂柱塞泵A10VSO 28排量：
A10VSO28DR/31R-PPA12N00
A10VSO28DR/31R-PPA12K01
A10VSO28DFR1/31R-PPA12N00
A10VSO28DFR1/31R-PPA12N00
A10VSO28DFR1/31R-PPA12K01
A10VSO28DFR/31R-PPA12N00
A10VSO28DFLR/31R-PPA12N00
A10VSO28DG/31R-PPA12N00
A10VSO28DRG/31R-PPA12N00
A10VSO28DFE1/31R-PPA12N00
A10VSO28FHD/31R-PPA12N00
A10VSO28ED/31R-PPA12N00

德國力士樂柱塞泵A10VSO 45排量：
A10VSO45DR/31R-PPA12N00
A10VSO45DR/31R-PPA12K01
A10VSO45DFR1/31R-PPA12N00
A10VSO45DFR1/31R-PPA12N00
A10VSO45DFR1/31R-PPA12K02
A10VSO45DFR/31R-PPA12N00
A10VSO45DFR/31R-PPA12K01
A10VSO45DFR/31R-PPA12K26
A10VSO45DFLR/31R-PPA12N00
A10VSO45DG/31R-PPA12N00
A10VSO45DRG/31R-PPA12N00
A10VSO45DFE1/31R-PPA12N00
A10VSO45FHD/31R-PPA12N00
A10VSO45ED/31R-PPA12N00
德國力士樂柱塞泵A10VSO 71排量：
A10VSO71DR/31R-PPA12N00
A10VSO71DR/31R-PPA12K01
A10VSO71DFR1/31R-PPA12N00
A10VSO71DFR1/31R-PPA12N00
A10VSO71DFR1/31R-PPA12K02
A10VSO71DFR/31R-PPA12N00
A10VSO71DFR/31R-PPA12K27
A10VSO71DFLR/31R-PPA12N00
A10VSO71DG/31R-PPA12N00
A10VSO71DRG/31R-PPA12N00
A10VSO71DFE1/31R-PPA12N00
A10VSO71FHD/31R-PPA12N00
A10VSO71ED/31R-PPA12N00
德國力士樂柱塞泵A10VSO 100排量：
A10VSO100DR/31R-PPA12N00
A10VSO100DR/31R-PPA12K01
A10VSO100DFR1/31R-PPA12N00
A10VSO100DFR1/31R-PPA12N00
A10VSO100DFR1/31R-PPA12K01
A10VSO100DFR/31R-PPA12N00
A10VSO100DFLR/31R-PPA12N00
A10VSO100DG/31R-PPA12N00
A10VSO100DRG/31R-PPA12N00
A10VSO100DFE1/31R-PPA12N00
A10VSO100DFE1/31R-PPA12K02
A10VSO100FHD/31R-PPA12N00
德國力士樂柱塞泵A10VSO 140排量：
A10VSO140DR/31R-PPB12N00
A10VSO140DR/31R-PPB12K01
A10VSO140DFR1/31R-PPB12N00
A10VSO140DFR1/31R-PPB12N00
A10VSO140DFR1/31R-PPB12K01
A10VSO140DFR/31R-PPB12N00
A10VSO140DFLR/31R-PPB12N00
A10VSO140DG/31R-PPB12N00
A10VSO140DRG/31R-PPB12N00
A10VSO140DFE1/31R-PPB12N00
A10VSO140DFE1/31R-PPB12N002
A10VSO140FHD/31R-PPB12N00
A10VSO140ED/31R-PPB12N00
以上為德國力士樂A10VSO型號 (31和52系列)無通軸型柱塞泵10、18、28、45、71、100、140各排量常規(guī)型號。