Hydraulic Valves

Hydraulic Valves

Hydraulic Valves

What is a Hydraulic Valve?

It is a circuit element that determines the direction of the hydraulic fluid, changes its direction when desired, and controls the pressure and flow rate of the fluid.

What are the Functions of Hydraulic Valves?

It opens and closes the path of the fluid.
It changes the direction of the fluid.
It sends the fluid to the tank.
It adjusts the operating speed of the receivers by controlling the flow rate of the fluid.
It protects circuit elements against high pressures. It sends the fluid whose pressure rises to the tank.
By controlling the pressure of the fluid, it ensures that circuit elements operate at certain pressures.
It controls the pressure, flow rate and direction of the fluid at certain time intervals.
Some valves can perform one or more of the tasks listed above.
PRESSURE CONTROL VALVES

These are valves used in the pressure lines of hydraulic systems, ensuring that the pressure of the fluid is at the desired value.

Types According to Their Used Places;

a) Pressure Relief valves
b) Pressure reducing valves
c) Pressure sequencing valves
d) Relief valves
Pressure Relief Valves

It allows enough pressure to overcome the resistance to perform the work. It sets a limit on the resistance that can occur above it ( = end of stroke).

PRESSURE REDUCING VALVES

It may be necessary to use more than one user element (cylinder, hydromotor) in hydraulic circuits to operate at different pressures, and the user elements may need to operate at different pressures. In such cases, pressure reducing valves are used. It is normally open. When the pressure rises, it switches to the closed position. There are different types, two-way and three-way.

PRESSURE SEQUENCING VALVES

Pressure sequence valves are used to operate multiple user elements such as cylinders and engines in a hydraulic circuit at different times and pressures. The working principle is similar to pressure relief valves. It is normally closed. It opens at the desired pressure and activates other user elements.

PRESSURE SEQUENCING VALVES

Pressure sequence valves are used to operate multiple user elements such as cylinders and engines in a hydraulic circuit at different times and pressures. The working principle is similar to pressure relief valves. It is normally closed. It opens at the desired pressure and activates other user elements.

DRAIN VALVES

It is used to send hydraulic fluid to the Hydraulic Tank. The valve, which is normally closed, opens when a warning comes and sends the fluid to the tank.

DIRECTIONAL CONTROL VALVES

These are valves that determine when and which path the fluid should follow in hydraulic circuits. They change the flow path when desired; They open and close the flow path when desired.

SCHEMATIC REPRESENTATION OF DIRECTIONAL CONTROL VALVES

Each position of the valve should be indicated by a square.
The passage directions of the fluid are indicated by arrows.
Road closures are designated by a horizontal line.
Valve connections are indicated by dashes.
Marking valve positions; valve positions are marked with letters from left to right. In three-position valves, the center position is indicated by 0.
CHECK VALVES

Check valves are hydraulic circuit elements that allow hydraulic fluid to pass in one direction.

Lettering of valve connections;

P=Pressure line A,B,C....=Work line or working line
R,S,T=Warehouse (return) line
X,Y,Z=Pilot (warning) line
L=Leakage line
Identification of directional control valves;

2 / 2 = Number of paths / Number of locations
When 3/2 valve is defined, it is understood that the valve is 3-way, 2-position.
Normal positions of valves;

In hydraulic circuit drawings, valves are drawn and lettered in their normal positions.
What Causes Hydraulic Valve Failures?

There are some problems that occur again and again during operation. The most common of these are:

Bad control element

excessive leakage

Broken or broken springs

Adhesion and seizing

Cracked or broken parts

Most valve failures occur due to problems elsewhere in the system.

Unless the actual fault is corrected, you can expect recurrence of faults with repaired or replaced valves.

Control of Hydraulic Valves

General inspection of parts; It includes visual inspection of defects such as protrusions, cuts, roughness, nicks, cracks, wear marks or bent parts.

Symptoms of Hydraulic Valve Malfunctions

Mud:   Substance formed by oxidation due to overheating of hydraulic fluid.

Scratch:   Small channels formed by wear on the surface of a valve   by high pressure fluid.

Knock:  Noise, hum, hum resulting from the control lead repeatedly hitting the solenoid body due to insufficient or excessive current.

When you disassemble a valve for repair or maintenance, always install a new one, even if all seals appear to be in good condition.

FLOW CONTROL VALVES

These are valves used to adjust the fluid flow rate in hydraulic systems. By changing the flow amount, we can adjust the speed of the cylinders and the speed of the engines. Flow control valves Cause significant pressure drop; Therefore, large amounts of heat are released. The flow rate is adjusted by changing the flow cross-section with the help of the adjustment screw.

Throttle Valve

These are circuit elements used to adjust the speed of the cylinders used in hydraulic systems or the speed of the hydromotor.

Check Valve Throttle Valves

Allows flow in both directions. Since the fluid flowing from left to right cannot pass through the check valve, it passes through the throttling section in a reduced amount. Fluid coming from the other direction passes easily by opening the check valve. These types of valves are used to quickly return the cylinders to the reverse position.