Discusión sobre los sesgos de memoria en la ansiedad (Estudio 1)

They­are­valves­which­permit­flow­in­one­direction­and­block­flow­in­the­opposite­direction.

Design:

The check valve basically consists of a housing with integrated valve seat, a cut and tempered cone and a pressure spring. The valve is also being produced with a ball as a closing element.

Function:

As­and­when­fluids­flow­through­the­valve­a­force­generated­by­the­system­pressure­acts­on­the­closing­element,­which­

works against the spring force. When this force exceeds the spring force, the closing element, in this case a cone, and releases­the­flow­from­B­to­A.­If­there­is­a­volume­flow­from­A­to­B,­the­cone­is­pushed­into­the­sealing­lip­and­seals­the­

valve without loss of leakage oil.

Fig. Check valve (RV)

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In­a­design­without­spring­it­is­important­that­the­valve­is­fitted­vertically.­This­way­the­deadweight­of­the­cone­helps­to­let­

it sit in the neutral position.

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housing seat valve

seat valve cone

Fig. Cone-seat Fig. Ball-seat Fig. Disc-seat

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Design:

HYDAC offers check valves in the following designs:

•­pipe­fitting­(rv)

•­sandwich­design­(rvp)

•­valves­in­a­threaded­plug­(RV­and­RVE)

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Please note:

The opening pressure of the valve is increased by the pressure at port A.

Model code:

The model code is composed of the following sequences:

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113 4.1.2 Pilot operated check valves

Design:

Hydraulic­pilot­operated­check­valves­can­be­opened­via­an­additional­pilot­oil­connector­for­flow­in­the­opposite­­direction.­

They consist of a housing, control spool, a valve seat, a ball and a closing spring.

Function:

The­valve­permits­free­flow­from­2­to­1­in­the­direction­of­flow.­In­the­opposite­direction­the­ball­is­pushed­on­the­valve­

seat­by­the­closing­spring­and­the­pressure­at­port­1­and­thus­blocks­the­flow­direction­from­1­to­2­without­loss­of­l­eakage­

oil. The pressure at port 1 acts on the control spool and counteracts the pilot pressure at port 3. Therefore during the hydraulic­opening­port­1­has­to­be­without­pressure.­If­the­pilot­pressure­at­port­3­is­sufficiently­high­the­piston­is­moved­

and­the­ball­is­pushed­away­from­the­valve­seat.­Now­the­valve­is­unblocked­and­fluid­can­flow­from­1­to­2.­The­return­

spring­fitted­underneath­the­piston­permits­an­undelayed­back­switch­once­the­pressure­is­lowered.

Fig. Hydraulically pilot operated check valve (ERVE)

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Please note:

The existing pressure countervails the opening pressure at port 3.

housing

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piston

return spring

ball

closing

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2 3

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Application:

With hydraulically pilot operated check valves, creeping movements in cylinders, which are operated by spool valves and which are loaded, can be prevented.

The valve is located in the return line of the cylinder and prevents the cylinder from extending even more under loading.

Only as and when pressure is built up in the feed line, the pilot control unit unblocks the check valve in the return line of the cylinder.

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Fig. Circut diagram: hydraulically pilot operated check valve (ERVE)

115 4.1.3 Check valves with pre-decompression

Description:

By opening a check valve a sudden opening of the entire cross section might happen. Decompression shocks might occur­with­high­volume­flow,­which­not­only­produce­a­lot­of­noise,­but­also­might­be­harmful­to­the­entire­unit.­Damage­

to­screwed­fittings­and­valves­could­be­the­result.

Function:

In order to prevent this, you could choose valves with preopening features. If pressure acts on the piston, it pushes down on the preopening ball. Only a small part of the cross section is opened. Only then the main cone is pushed off its seat.

This­way­a­smooth­release­of­the­pressurized­fluid­is­possible.

Fig. Pilot operated check valve with predecompression (ERVE-R1)

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piston

check valve

closing spring housing

ball

piston

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Model code:

The model code is composed of the following sequences:

Pre-decompression:

•­for­large­volume­flows

•­for­very­high­pressures­(otherwise­the­unit­will­become­too­large)

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Please note:

The existing pressure countervails the opening pressure at port 3.

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117 4.1.4 Lowering speed controlled valves

Description:

Lowering speed controlled valves belong to the group of check valves. These are valves whose block position is canceled by a hydraulic operation or if the pre-set pressure has been reached.

They fulfil the following tasks:

Fig. Lowering speed controlled valves (SBVER1) Application:

Lowering speed controlled valves in combination with double acting actuators, like cylinders and hydraulic motors, are

­mainly­used­for­safety­measures­and­control­functions.­They­have­to­fitted­at­the­outlet­side­of­each­actuator,­because­of­

a possible reversal of the load and direction of movement.

Lowering speed controlled valves help to control the lowering of loads and also work as a speed control mechanism. They also serve as a safety measure if loads have to be held in place in case of pipe and hose bursts.

Function:

Lowering speed controlled valves are directly controlled piston seat valves for oil-hydraulic tasks. They permit a smooth moving of actuators for pulling and pushing loads.

These valves basically consist of a housing, check valve piston (RV-piston), closing spring, adjustment spring, adjustment unit for presetting of spring force and a cut and tempered control piston.

For­lifting­loads­fluids­flow­from­port­2­to­1­of­the­in-built­check­valve.­The­RV-piston­is­moved­against­the­closing­spring­

and­opens­the­appropriate­cross­section­for­the­fluid­flow.

If the valve is closed the actuator is held in its present position. The RV-piston is pushed against the control piston and seals at the seat edge. You have to make sure that control port 3 is not under pressure when the valve is closed.

The pressure at the actuator (load pressure) at port 1 acts upon the control piston area A1 and thus against the force of the adjustment spring. This way a limitation of the load pressure can be achieved. The maximum preset pressure at the actuator should always be at least 20% above the highest load pressure permitted for standard operations.

When­the­load­is­lowered­(volume­flow­from­port­1­to­port­2)­the­valve­is­being­acted­upon­via­port­3.­the­volume­flow­of­

the load is controlled at the spool land of the control piston. A sudden drop of the load is thus prevented.

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Example:

Fig. Lowering speed controlled valve

The opening point of a lowering speed controlled valve can be calculated by means of the following formula:

p₁­ =­ highest­pressure­to­move­the­max.­load­(load­pressure)­in­bar p₂­ =­ pressure­at­connection­2­in­bar

p3,erf­ =­ required­control­in­bar­at­connection­3­to­unlatch p_e­ =­ adjusting­pressure­in­bar­(p_e ≥p₁­•­1,2)

Please note:

Pressure at p₂ is incorporated as disturbance variable!

Pilot ratio:

Pilot ratio φ:

Pilot ratio is a very important parameter in selecting the right valve. The pilot ratio should be selected in such a way, that an­excellent­load­control­is­possible­with­an­energy­loss­as­low­as­possible.­It­depends­first­and­foremost­on­its­applica-tion. In order to obtain good dynamic properties, valves with high pilot ratio are applied in hydraulic motor applications. It is the other way round with the application of cylinders, where small pilot ratios are preferred.

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119 4.1.5 Twin check valves

Design:

If you combine two pilot operated check valves you get a twin check valve. Built into a hydraulic unit it prevents cylinders from re-traction or extension due to external forces. The circuit diagram down below shows how it works.

Function:

The hydraulic check valve RPDR06 is a twin check valve in one housing, consisting of 2 check valves, which allow the volume­flow­only­in­one­direction.­The­volume­flow­in­the­other­direction­is­reversed­through­the­other­valven.

Fig. Twin check valves (RPDR06) Function hydraulic diagram:

Let­us­assume­a­free­volume­flow­in­flow­direction­A₁ to A₂ and B₁ to B₂ respectively. In the direction A₂ to A₁ and B₂ to B₁­the­valves­block­the­volume­flow.­Therefore­the­cylinder­cannot­be­moved­due­to­external­forces.

Now­if­you­set­the­directional­valve­in­a­way­that­the­cylinder­can­extend­the­volume­fluid­can­flow­freely­from­B₁ to B₂. Thus the pressure line to the second valve is activated and the valve opens. The line from A2 to A1 is set free. The cylinder can extend without any problems.

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Fig. Circut diagram: twin check valves (RPDR06)

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4.1.6 Pipe bursting protection

In document Influencia de la ansiedad en el recuerdo de información emocional : meta-análisis sobre los sesgos de memoria y su estudio en personas mayores (página 101-105)