EP2005006B1

EP2005006B1 - Pilot-operated differential-area pressure compensator and control system for piloting same

Info

Publication number: EP2005006B1
Application number: EP07727891A
Authority: EP
Inventors: Gianluca Ganassi
Original assignee: Walvoil SpA
Current assignee: Walvoil SpA
Priority date: 2006-04-12
Filing date: 2007-04-06
Publication date: 2010-09-29
Anticipated expiration: 2027-04-06
Also published as: WO2007116035A1; ATE483111T1; DE602007009509D1; EP2005006A1; ITPR20060036A1

Abstract

In a hydraulic Load Sensing directional control valve, a pressure compensator, bypass-connected to the delivery line, discharges the pump-delivered fluid flow not demanded by the actuators to the low-pressure line, with a first (lower) value or a second (higher) value of pressure margin, depending on how one of its differential areas is piloted by a hydraulic, mechanical or electrohydraulic control system.

Description

The present invention relates to a differential-area pressure compensator and to its control system of the hydraulic, mechanical or electro-hydraulic type.
Directional control valves, for controlling the fluid flow delivered to actuators regardless of pressure, are widely used in hydraulics.
Such valves are commonly known as load sensing directional control valves or load sensing control valves.
Flow sharing valves are a subset of these load sensing control valves.
They behave like any other load sensing control valve when the pump delivers enough flow to meet the demand of the actuators; in addition, when the system is in a flow saturation condition, they distribute the pump-delivered flow to all operating ports proportionally to their demand, without causing any operating actuator to stop.
A detailed description of the operating principle of a particular load sensing, flow sharing system is found in US2006037649 or US 3 937 129 .
Load sensing control valves are of the closed center or open center type.
When no actuator is operated, i.e. in the standby state, open center load sensing control valves discharge all the flow delivered by the pump, while closed center control valves do not.
For this purpose, open center load sensing control valves have a pressure compensator bypass-connected to the delivery line, which discharges the pump-delivered fluid flow not demanded by the actuators; if the overall flow demanded by the actuators does not exceed the flow delivered by the pump, then the pressure compensator discharges the flow not demanded by the actuators at a delivery pressure that is equal to the higher pressure among the served ports, usually named LS pressure, plus a pressure margin depending on the compensator spring, e.g. 14 bar.
In the standby state, an open center load sensing control valve wastes a non negligible amount of power, equal to the flow delivered by the pump multiplied by the pressure margin .
DE 10 2004 014 113 A1 discloses a device for reducing the pressure margin in the standby state, thereby providing energy savings.
Next to the pressure compensator 10, which imposes a pressure margin of 21 bar, there is a pilot-operated compensator 12 which imposes a pressure margin of 3 bar and is controlled by an LS pressure-controlled pilot valve 17.
When none of the actuators requires flow , i.e. the LS pressure is zero, the pressure compensator 12 discharges all pump-delivered flow at the pressure of 3 bar, because the pressure on the spring side 13 is the discharge pressure, the pilot valve 17 being open; the pressure compensator 10 is closed because the delivery pressure does not reach 21 bar.
When at least one actuator requires oil, i.e. when the LS pressure is greater than zero, the pressure compensator 12 is in the closed position because the pressure on the spring side 13 is the delivery pressure, the pilot valve 17 being closed; the pressure compensator 10 discharges the flow not demanded by actuators at the pressure of 21 bar plus the LS pressure.
This system involves an increased number of compensators as well as a more complex construction, thereby leading to cost increase: the above mentioned patent application requires two compensators, operating at different pressure values.
In this invention a valve, bypass-connected to the delivery line in a load sensing control valve, discharges the pump-delivered fluid flow not demanded by the actuators to the low pressure line, at a first (lower) value or a second (higher) value of pressure margin, depending on how the valve is controlled by a hydraulic, mechanical or electrohydraulic control system.
According to a first way of carrying out the pressure compensator with differential areas controlled by a control system, the compensator is normally closed; it is biased closed by a spring and by the LS pressure; it is biased open by two pressures respectively exerted on two appropriately determined different areas, one subjected to the delivery pressure and the other to the delivery pressure or the LS pressure depending on the control system.
A first object of the present invention is to save energy in the standby state, by decreasing the pressure margin from the operating state to the standby state and increasing the pressure margin in the opposite case.
For this first object to be fulfilled, the control system is a three-way two-position hydraulically actuated pilot valve, which is biased on one side by the LS pressure and on the other side by a spring having a pressure rating of about 2 bar and by the discharge pressure: when the LS pressure is zero, the pilot valve transmits the delivery pressure to the compensator area controlled thereby; when the LS pressure is not zero, it transmits the LS pressure.
A second object of the present invention is specific for load sensing, flow sharing systems and consists in allowing the operator to select slow or fast operation of the machine, for normal or fine motion of the actuators.
For this second object to be fulfilled, the control system is a three-way, two-position mechanically or electrically actuated pilot valve which, like the hydraulic pilot valve described above, transmits either the delivery pressure or the LS pressure to the compensator area controlled thereby.
A third object of the present invention is specific for load sensing, flow sharing systems and consists in simultaneously fulfilling the first and the second objects.
For this third object to be fulfilled, the control system is a three-way, two position hydraulically actuated pilot valve, combined with a three-way two-position mechanically or electrically actuated pilot valve: the hydraulically actuated pilot valve is biased on one side by the LS pressure and on the other side by a spring having a pressure rating of about 2 bar and by the discharge pressure so that, when the LS pressure is zero, it transmits the delivery pressure, and when the LS pressure is not zero, it transmits the LS pressure to the solenoid valve. The mechanically or electrically actuated pilot valve in turn transmits the delivery pressure or the pressure it receives from the hydraulically actuated three-way two-position pilot valve to the compensator area controlled thereby.
According to a second way of carrying out the pressure compensator with differential areas controlled by a control system, the compensator is normally closed; it is biased open by the delivery pressure; it is biased closed by a spring and by two pressures respectively exerted on two appropriately determined different areas, one subjected to the LS pressure and the other to the delivery pressure or the LS pressure depending on the control system.
Once again, in the second way of carrying out the pressure compensator with differential areas, the control system can be designed to fulfill the first, second, or third objective.
These objects and advantages are achieved by the control systems for piloting the pilot-operated differential-area pressure compensator according to this invention, which is characterized by the annexed claims.
These and other features will be more apparent from the following description of a few embodiments, which are shown by way of example and without limitation in the accompanying drawings, in which:

Figure 1 is a hydraulic diagram showing a first way of carrying out the differential-area pressure compensator piloted by a control system, in which the control system is a three-way two-position hydraulically actuated pilot valve;
Figure 2 is a hydraulic diagram showing a variant of the control system of the pilot-operated differential-area pressure compensator of Figure 1, in which the control system is a three-way two-position electrically actuated pilot valve;

Figure 3 is a hydraulic diagram showing a variant of the control system of the pilot-operated differential-area pressure compensator as shown in Figures 1 and 2, in which the control system is a three-way two-position hydraulically actuated valve in combination with a three-way two-position electrically actuated pilot valve;
Figure 4 is a hydraulic diagram showing a second way of carrying out the differential-area pressure compensator piloted by a control system, in which the control system is a three-way two-position hydraulically actuated pilot valve;
Figure 5 shows a first embodiment according to the first way of carrying out the differential-area pressure compensator shown in Figure 1;
Figure 6 shows a second embodiment according to the second way of carrying out the differential-area pressure compensator shown in Figure 4.

Figure 1 shows a hydraulic circuit, including a fixed-displacement pump 1, connected by a high-pressure line P to a load sensing, flow sharing control valve V, which discharges the fluid through a low pressure line T into the tank 2.
The load sensing, flow sharing control valve V has an inlet cover F and two elements or sections E1 and E2, each controlling an actuator through the ports A1, B1 and A2, B2.
A detailed description of the specific configuration of the load sensing, flow sharing control valve V shown in figure may be found in patent application US2006037649 A1 by the applicant hereof, therefore its architecture and working principle will be only described shortly herein.
Each element has a spool 4, a local pressure compensator 3 comprising therein a signal selector S, which is mechanically kept open or closed by a piston 5 with a spring M of negligible force. The piston 5 presses against the compensator 3 of the element E at the higher pressure in the control valve V, said compensator 3 and piston 5 thus acting as a check valve, whereas, in the sections at lower pressure, the piston 5 is kept detached from the compensator 3, so that this latter performs its function of pressure compensator.
As a rule, the amount of fluid flowing through an orifice is proportional to the area of the orifice and to the square root of the pressure drop thereacross, assuming the other factors are equal.
In load sensing, flow sharing control valves, flow rate is controlled by adjusting the position of the spool, as the effective pressure drop across the flow rate control or metering orifice of each spool is the same for all elements and is equal to pressure margin, regardless of the pressure of loads. Pressure margin is a quasi constant value under flow unsaturated conditions and decreases as saturation occurs.
Inside the inlet cover F, the high pressure line P is connected to the low pressure line T through the differential-area pressure compensator C piloted through the control line 15 by the control system S.
The compensator C is a two-way continuous position valve 6, which is biased closed by a spring 7 and by the LS pressure exerted on the surface 8, and is biased open by the pressure P exerted on the surface 9 and the control pressure of line 15 on the surface 10.
Assuming that A8 designates the area of the control surface 8, A9 designates the area of the control surface 9 and A10 designates the area of the control surface 10, the valve 6 is designed in such a manner that the sum of the areas A9 and A10 is equal to the area A8 of the control surface 8: A9+A10=A8
The valve 6 can be designed in various manners within the functional arrangement as set out above.
Figure 5 shows a first embodiment according to the first way of carrying out the differential-area pressure compensator shown in fig. 1.
The control system S is a three-way, two-position pilot valve 11, whose spool is piloted on the surface 13 by the pressure T and is biased by a spring 12 whose force against the area of the control surface corresponds to about 2 bar; on the other surface 14 it is controlled by the LS pressure.
The pilot valve 11 normally transmits the pressure P to the surface 10 of the valve 6 through the control line 15, and it transmits the LS pressure when it is switched.
The differential-area compensator C, piloted by the control system S of Figure 1 sets the pressure margin to a first value from 3 to 7 bar, e.g. 5 bar, if the operator does not actuate any spool, or to a second value from 14 to 25 bar, e.g. 14 bar, if the operator actuates at least one spool, thereby allowing to save energy in the standby state.
In the standby state, the LS pressure is zero, as no spool is operated. The pilot valve 11 is in the position depicted in Figure 1 due to the bias of the spring 12, and transmits the pressure P to the surface 10 of the valve 6 through the line 15.
Assuming that F7 designates the force of the spring 7, p_P is the delivery pressure and p_LS the LS pressure, then the balance of the valve 6 is given by the following relation: $p_{LS} \cdot A 8 + F 7 = p_{P} \cdot A 9 p_{P} \cdot A 10$
Considering the relations between the areas: $p_{p} - p_{LS} = {}^{F 7}{/_{A 8}}$
Thence, the pressure margin p_P - p_LS is equal to a first value, corresponding to F7 / A8, in this example to 5 bar: therefore, in the standby state, the differential-area compensator C controlled by the control system S of Figure 1 discharges the whole flow delivered by the pump 1 at a pressure of 5 bar.
When the operator actuates at least one spool, the LS pressure increases and switches the pilot valve 11, whereby the control system S pilots the surface 10 of the valve 6 through the control line 15 with the LS pressure.
The balance of the valve 6 in this operating state is given by the following relation: $p_{LS} \cdot A 8 + F 7 = p_{P} \cdot A 9 p_{LS} \cdot A 10$
Whence: $p_{p} - p_{LS} = {}^{F 7}{/_{A 9}}$
Since A9 is smaller than A8, the second pressure margin value p_P - p_LS, in this example 14 bar, is higher than the former, therefore in operating conditions the differential-area compensator C controlled by the control system S of Figure 1 discharges the pump-delivered flow not demanded by the active workports at a pressure pp 14 bar higher than P_LS.
Figure 2 shows a load sensing, flow sharing control valve V comprising a pilot-operated differential-area pressure compensator C as shown in Figure 1, in which the control system S is a three-way two-position electrically actuated spool 17.
The spool 17 normally transmits the LS pressure through the control line 15 and, in the excited position, it transmits the pressure P.
Thus, the control system S allows to set the pressure margin to two values, e.g. 5 and 14 bar.
In load sensing, flow sharing control valves, the flow to the port is proportional to the square root of the pressure margin, assuming the other factors are equal, therefore if the pressure margin decreases, flows to the workports are accordingly reduced, for finer control of the machine.
In this case, unlike the configuration of Figure 1, pressure margin control depends on the position of the electrically actuated spool 17, therefore on the operator, who can select normal speed (normal control) or reduced speed (fine control) of the machine actuators.
The operating principle is unchanged if the three-way two-position spool 17 is mechanically or electrically controlled.
Figure 3 shows a load sensing, flow sharing control valve V comprising a pilot-operated differential-area pressure compensator C as shown in Figures 1 and 2, and a control system S in the form of a three-way two-position hydraulically actuated pilot valve 18 in combination with a three-way two-position electrically actuated spool 22.
The spool of the pilot valve 18 is piloted on the surface 20 by the pressure T and is biased by a spring 19 whose force against the area of the control surface corresponds to about 2 bar; on the other surface 21 it is controlled by the LS pressure. The pilot valve 18 normally transmits the pressure P to the spool 22 through the line 23, and it transmits the LS pressure when it is switched.
The spool 22 normally connects the line 23 to the control line 15 and, in the excited position, it transmits the pressure P to the control line 15.
When the spool 22 is in the position shown in figure 3, the differential-area compensator C, controlled by the control system S , sets the pressure margin to a first value, e.g. 5 bar, if the operator does not actuate any spool, or to a second value, e.g. 14 bar, if the operator actuates at least one spool, thereby allowing to save energy in the standby state; when the operator switches the spool 22, the pressure margin is set to the first 5 bar value even in operating conditions, for fine control of the machine actuators.
In Figure 4, the high pressure line P is connected to the low pressure line T through the differential-area pressure compensator C piloted through the control line 33 by the control system S.
The compensator C is a two-way continuous position valve 24, which is biased open by the pressure P exerted on the surface 28, and is biased closed by a spring 25, by the control pressure of 33 exerted on the surface 26 and by the LS pressure on the surface 27.
Assuming that A26 designates the area of the control surface 26, A27 designates the area of the control surface 27 and A28 designates the area of the control surface 28 the valve 24 is designed in such a manner that: $A 28 = A 26 + A 27$
The valve 24 can be designed in various manners within the functional arrangement as set out above.
Figure 6 shows an embodiment according to the second way of carrying out the differential-area pressure compensator shown in fig. 4.
The control system S is a three-way, two-position pilot valve 29, whose spool is piloted on the surface 31 by the discharge pressure p_T and is biased by a spring 30 whose force against the area of the control surface corresponds to about 2 bar; on the other surface 32 it is piloted by the LS pressure. The pilot valve 29 normally transmits the LS pressure to the surface 26 of the valve 24 through the control line 33, and it transmits the pressure pp when it is switched.
The differential-area compensator C, controlled by the control system S of Figure 4 sets the pressure margin to a first value from 3 to 7 bar, e.g. 5 bar, if the operator does not actuate any spool, or to a second value from 14 to 25 bar, e.g. 14 bar, if the operator actuates at least one spool, thereby allowing to save energy in the standby state.
In the standby state, the LS pressure is zero, as no spool is operated. The pilot valve 29 is in the position depicted in Figure 4 due to the bias of the spring 30, and transmits the LS pressure to the surface 26 of the valve 24 through the line 33.
Assuming that F25 designates the force of the spring 25, then the balance of the valve 24 is given by the following relation: $p_{LS} \cdot A 26 + p_{LS} \cdot A 27 + F 25 = p_{P} \cdot A 28$
Whence: $p_{p} - p_{LS} = {}^{F 25}{/_{A 28}} \cdot$
The pressure margin pP - pLS is equal to a first value, corresponding to F25 / A28, in this example to 5 bar, therefore, in the standby state, the differential-area compensator C controlled by the control system S of Figure 4 discharges the whole flow delivered by the pump 1 at a pressure of 5 bar.
When the operator actuates at least one spool, the LS pressure increases and switches the valve 29, whereby the control system S pilots the surface 26 of the valve 24 through the line 33 with the pressure pP.
The balance of the valve 6 in this operating state is given by the following relation: $p_{p} \cdot A 26 + p_{LS} \cdot A 27 + F 25 = p_{P} \cdot A 28$
Whence: $p_{p} - p_{LS} = {}^{F 25}{/_{A 27}}$
Since A27 is smaller than A28, the second pressure margin value pP - pLS is higher than the former, in this example 14 bar, therefore in operating conditions the differential-area compensator C piloted by the control system S of Figure 4 discharges the pump-delivered flow not demanded by the workports at a pressure pP 14 bar higher than pLS.
The control systems described above for the compensator according to the first way of carrying out the present invention can be easily used for the compensator of the second way of carrying out the present invention.
Figure 5 shows an embodiment according to the first way of carrying out the differential-area pressure compensator shown in Figure 1.
A passage 106 is formed in the body 108 of the inlet cover F, whose section has an area A8 and within which the valve 6 slides between two plugs 115 and 116.
Two annular recesses 105 and 103 are provided within the passage 106: the recess 105 receives pressurized fluid through the high pressure P line from the pump 1; the recess 103 is connected to the tank 2 through the low pressure T line.
The valve 6 normally closes the connection between the recesses, 105 and 103 because its edge 111 covers the edge 110 of the body 108.
The spring 7 operates in the closing direction on the surface 8 of the valve 6 in combination with the LS pressure reigning in the chamber 107, which is delimited by the surface 8, the body 108 and the plug 116.
A bore 114, whose section has an area A9, is formed in the valve 6, on the opposite side of the surface 8.
A piston 100, sliding within the bore 114, has two surfaces at its ends, the surface 112 on the side of the valve 6, and the surface 101 on the side of the plug 115.
The piston 100 delimits a chamber 113 between the surface 112 and the surface 9, in which there is the pressure P, thanks to the holes 109 and 104 in the valve 6.
The surface 10 of the valve 6 and the surface 101 of the piston 100, with the body 108 and the plug 115, delimit the chamber 102, which receives the control pressure of the valve 11 through the line 15.
When in the chamber 102 there is the LS pressure, the piston 100 is biased against the plug 115 by the pressure pP in 113, and when in the chamber 102 there is the pressure pP, the piston 100 is in neutral equilibrium. In both cases, the piston 100 exerts no force on the valve 6, whose balanced state is determined by the pressures exerted on the surfaces 8, 9 and 10 and by the spring 7, as explained in the description of Figure 1.
Figure 6 shows an embodiment according to the second way of carrying out the differential-area pressure compensator shown in Figure 4.
A bore 211 is formed in the body 209 of the inlet cover F, whose section has an area A27 and within which the valve 204 slides.
Two recesses 205 and 203 are provided within the bore 211: the recess 205 receives pressurized fluid through the high pressure P line from the pump 1; the recess 203 is connected to the tank 2 through the low pressure T line.
The valve 204 normally closes the connection between the recess 205 and the recess 203 because its edge 208 covers the edge 207 of the body 209.
The spring 25 operates in the closing direction on the surface 27 of the valve 204 in combination with the LS pressure reigning in the chamber 206, which is delimited by the surface 27, the plug 215 and the body 209.
In the body 209, opposite to the surface 27, there is a passage 210, of greater diameter than the bore 211, whose section has an area A28.
A piston 201 slides within the bore 210 and has two surfaces at its ends, the surface 212 on the side of the valve 204, and the surface 28 on the side of the plug 214.
The piston 201 delimits a chamber 200 with the surface 28, the body 209 and the plug 214, with the delivery pressure pP therein.
The surface 213 of the valve 204, the valve 204 itself and the surface 212 of the piston 201, with the body 209, delimit the chamber 202, which receives the control pressure of the valve 29 through the line 33.
When the pressure in the chamber 202 is the delivery pressure pP, the piston 201 is in neutral equilibrium. In this case, if A213 designates the area of the projection of the surface 213 on a plane normal to the axis of the valve 204, the balance in the axial direction of the valve 204 is given by the following relation: $p_{p} \cdot A 213 = p_{LS} \cdot A 27 + F 25$
Since A213 = A27, then: $p_{p} - p_{LS} = {}^{F 25}{/_{A 27}}$
When the pressure in the chamber 202 is the LS pressure, the piston 201 is pushed against the valve 204 by the pressure pP in the chamber 200.
In this case, the valve 204 and the piston 201 are pressed one against the other and, assuming that A212 designates the area of the surface 212, they are in equilibrium in the following manner: $p_{p} \cdot A 28 + p_{LS} \cdot A 213 = p_{LS} \cdot A 212 + p_{LS} \cdot A 27 + F 25$
And since A213 = A27, A212 = A28: $p_{p} \cdot A 28 = p_{LS} \cdot A 28 + F 25$
In short, the operation of the preferred embodiment as shown in Figure 6 is similar to that explained in the description of Figure 4, in fact the piston 201 and the valve 204, even though separated components to avoid the need for any coaxial grinding, if thought as a single component lead to the valve 24 of Figure 4.

Claims

A differential-area pressure compensator (C) piloted by a control system (S), said control system (S) being of the hydraulic, mechanical or electro-hydraulic type, in a hydraulic load sensing control valve (V), comprising a high pressure (P) line, a low pressure (T) line, and a line (LS) at the LS pressure of the higher load, said two-way, continuous positioning, normally closed compensator (C) joining the high pressure (P) line with the low pressure (T) line, said compensator (C) discharging the pump-delivered fluid flow not demanded by the actuators to the low pressure (T) line, the pressure margin at which it discharges the pump-delivered fluid flow not demanded by the actuators being equal to a first value, from 3 to 7 bar, or a second value, from 14 to 25 bar, depending on how said differential-area compensator (C) is piloted by a control system (S), said compensator (C) being biased closed by the action of a spring (7) and the LS pressure on a first surface (8) and being biased open by the action of the delivery pressure (P) on a second surface (9) and by the pilot pressure transmitted by the control system (S) on a third surface (10), the sum of the areas of the latter two surfaces (9, 10) being equal to the area of the former (8) and the pilot pressure of the control system (S) being equal to the delivery pressure (P) or the LS pressure, characterized in that said control system (S) is a three-way two-position pilot valve (11) controlled by the LS pressure which, when the LS pressure is zero, transmits the delivery pressure to the surface (10) controlled thereby, whereas, when the LS pressure is not zero, transmits the LS pressure.
A differential-area pressure compensator (C) piloted by a control system (S), said control system (S) being of the hydraulic, mechanical or electro-hydraulic type, in a hydraulic load sensing control valve (V), comprising a high pressure (P) line, a low pressure (T) line, and a line (LS) at the LS pressure of the higher load, said two-way, continuous positioning, normally closed compensator (C) joining the high pressure (P) line with the low pressure (T) line, said compensator (C) discharging the pump-delivered fluid flow not demanded by the actuators to the low pressure (T) line, the pressure margin at which it discharges the pump-delivered fluid flow not demanded by the actuators being equal to a first value, from 3 to 7 bar, or a second value, from 14 to 25 bar, depending on how said differential-area compensator (C) is piloted by a control system (S), said compensator (C) being biased closed by the action of a spring (7) and the LS pressure on a first surface (8) and being biased open by the action of the delivery pressure (P) on a second surface (9) and by the pilot pressure transmitted by the control system (S) on a third surface (10), the sum of the areas of the latter two surfaces (9, 10) being equal to the area of the former (8) and the pilot pressure of the control system (S) being equal to the delivery pressure (P) or the LS pressure, characterized in that said control system (S) is a three-way two-position electrically or mechanically actuated pilot spool (17) which transmits the delivery pressure (P) or the LS pressure to the surface (10) controlled thereby.
A differential-area pressure compensator (C) piloted by a control system (S), said control system (S) being of the hydraulic, mechanical or electro-hydraulic type, in a hydraulic load sensing control valve (V), comprising a high pressure (P) line, a low pressure (T) line, and a line (LS) at the LS pressure of the higher load, said two-way, continuous positioning, normally closed compensator (C) joining the high pressure (P) line with the low pressure (T) line, said compensator (C) discharging the pump-delivered fluid flow not demanded by the actuators to the low pressure (T) line, the pressure margin at which it discharges the pump-delivered fluid flow not demanded by the actuators being equal to a first value, from 3 to 7 bar, or a second value, from 14 to 25 bar, depending on how said differential-area compensator (C) is piloted by a control system (S), said compensator (C) being biased closed by the action of a spring (7) and the LS pressure on a first surface (8) and being biased open by the action of the delivery pressure (P) on a second surface (9) and by the pilot pressure transmitted by the control system (S) on a third surface (10), the sum of the areas of the latter two surfaces (9, 10) being equal to the area of the former (8) and the pilot pressure of the control system (S) being equal to the delivery pressure (P) or the LS pressure, characterized in that said control system (S) is a three-way two-position valve (18) controlled by the LS pressure in combination with a three-way two-position electrically or mechanically actuated spool (22), the hydraulic pilot valve (18) transmitting to the spool (22) the delivery pressure (P) when the LS pressure is zero, or the LS pressure when the LS pressure is not zero, and the spool (22) transmitting in turn the delivery pressure (P) or the pressure it receives from the three-way two-position valve (18) controlled by the LS pressure to the surface (10).
A differential-area pressure compensator (C) piloted by a control system (S), said control system (S) being of the hydraulic, mechanical or electro-hydraulic type, in a hydraulic load sensing control valve (V), comprising a high pressure (P) line, a low pressure (T) line, and a line (LS) at the LS pressure of the higher load, said two-way, continuous positioning, normally closed compensator (C) joining the high pressure (P) line with the low pressure (T) line, said compensator (C) discharging the pump-delivered fluid flow not demanded by the actuators to the low pressure (T) line, the pressure margin at which it discharges the pump-delivered fluid flow not demanded by the actuators being equal to a first value, from 3 to 7 bar, or a second value, from 14 to 25 bar, depending on how said differential-area compensator (C) is piloted by a control system (S), said compensator (C) being biased open by the action of the delivery pressure (P) on a first surface (28) and being biased closed by the action of a spring (25), of the LS pressure on a second surface (27) and of the control transmitted by a control system (S) on a third surface (26), the sum of the areas of the latter two surfaces (27, 26) being equal to the area of the former (28) and the pilot pressure of the control system (S) being equal to the delivery pressure (P) or the LS pressure, characterized in that said control system (S) is a three-way two-position pilot valve (29) piloted by the LS pressure which, when the LS pressure is zero, transmits the LS pressure to the surface (26) controlled thereby, whereas, when the LS pressure is not zero, transmits the delivery pressure.
A differential-area pressure compensator (C) piloted by a control system (S), said control system (S) being of the hydraulic, mechanical or electro-hydraulic type, in a hydraulic load sensing control valve (V), comprising a high pressure (P) line, a low pressure (T) line, and a line (LS) at the LS pressure of the higher load, said two-way, continuous positioning, normally closed compensator (C) joining the high pressure (P) line with the low pressure (T) line, said compensator (C) discharging the pump-delivered fluid flow not demanded by the actuators to the low pressure (T) line, the pressure margin at which it discharges the pump-delivered fluid flow not demanded by the actuators being equal to a first value, from 3 to 7 bar, or a second value, from 14 to 25 bar, depending on how said differential-area compensator (C) is piloted by a control system (S), said compensator (C) being biased open by the action of the delivery pressure (P) on a first surface (28) and being biased closed by the action of a spring (25), of the LS pressure on a second surface (27) and of the control transmitted by a control system (S) on a third surface (26), the sum of the areas of the latter two surfaces (27, 26) being equal to the area of the former (28) and the pilot pressure of the control system (S) being equal to the delivery pressure (P) or the LS pressure, characterized in that said control system (S) is a three-way two-position electrically or mechanically actuated pilot valve, which transmits the delivery pressure (P) or the LS pressure to the surface (26) controlled thereby.
A differential-area pressure compensator (C) piloted by a control system (S), said control system (S) being of the hydraulic, mechanical or electro-hydraulic type, in a hydraulic load sensing control valve (V), comprising a high pressure (P) line, a low pressure (T) line, and a line (LS) at the LS pressure of the higher load, said two-way, continuous positioning, normally closed compensator (C) joining the high pressure (P) line with the low pressure (T) line, said compensator (C) discharging the pump-delivered fluid flow not demanded by the actuators to the low pressure (T) line, the pressure margin at which it discharges the pump-delivered fluid flow not demanded by the actuators being equal to a first value, from 3 to 7 bar, or a second value, from 14 to 25 bar, depending on how said differential-area compensator (C) is piloted by a control system (S), said compensator (C) being biased open by the action of the delivery pressure (P) on a first surface (28) and being biased closed by the action of a spring (25), of the LS pressure on a second surface (27) and of the control transmitted by a control system (S) on a third surface (26), the sum of the areas of the latter two surfaces (27, 26) being equal to the area of the former (28) and the pilot pressure of the control system (S) being equal to the delivery pressure (P) or the LS pressure, characterized in that said control system (S) is a three-way two-position hydraulic pilot valve controlled by the LS pressure, in combination with a three-way two-position manually or electrically actuated valve, the hydraulic pilot valve transmitting to the solenoid valve the LS pressure when the LS pressure is zero, or the delivery pressure (P) when the LS pressure is not zero, and the solenoid valve transmitting in turn the LS pressure or the pressure it receives from the three-way two-position valve controlled by the LS pressure to the surface (26).
A compensator (C) as claimed in claim 4 or 5 or 6, characterized in that, it is composed of a valve (204) and a piston (201) of greater diameter than the spool of the valve (204):
- said valve (204) being biased closed by the spring (25) and by the LS pressure, and biased open by the pilot pressure of the control system (S) and by the piston (201),

- said piston (201) being pushed on one side by the valve (204) and by the pilot pressure of the control system (S) and on the other side by the pressure of the high pressure (P) line.