Hydraulics circuits

1. DONE BY:
DOMINIC HENDRY
GOKUL
DINESH KUMAR
DANIEL JESHTUS

2. The counterbalance valve, also called a
holding valve, is used to prevent a
weight from falling uncontrollably. As
an example, consider a press with a
two-ton platen . When the directional
control is shifted, the platen will fall
unless there is a means for creating an
opposing hydraulic force. A
counterbalance valve accomplishes
this task.
Any pressure above 28 psi causes the
platen to move downward. Note that
the cylinder friction force was not
considered in this problem.
HYDRAULICS CYLINDER USING COUNTER
BALANCE CIRCUIT

3. Often, it is desirable to use the weight
of the platen to help build the total
pressing force. In this case, a
counterbalance valve with remote
pilot line connection is used (Fig. 3.28).
If pressure at the cap end, and thus the
pilot line, drops below the set point,
the counterbalance valve partly closes
to slow the platen.
There is an additional reason for using a counterbalance valve other than to
prevent uncontrolled motion of the actuator. When the platen is moving
down too fast, the pump cannot keep the cap end filled with fluid, and a
negative pressure can develop. It is possible to suck the fluid out of the
pump fast enough to cause void spaces in the pump. The condition when
the pump is not completely filled with fluid is called cavitations. One of the
problems caused by cavitations is a breakdown of the lubrication film
between moving parts. A higher pressure setting on the counterbalance
valve is needed to achieve the desired counterbalance and limit actuator
speed.

4. HYDRAULIC CYLINDER USING SEQUENCIAL
CIRCUIT
The circuit depicted in Figure 10.6
contains a hydraulic system in which
two sequence valves are used to
control the sequence of operation of
two double-acting cylinders.
When the DCV is shifted into its left
envelope mode, the left cylinder
extends completely and then the right
cylinder extends. If the DCV is shifted
into its right envelope mode, the
right cylinder retracts fully followed
by the left cylinder. This sequence of
the cylinder operation is controlled by the sequence valves. The spring
centered position of the DCV locks both the cylinders in place.

5. PRESSURE INTENSIFICATION:

6. FORCE MULTIPLICATION: