5. Recommendations
5.7. Recommendations for specific scenarios
Project 07:
Check valve Bosch Rexroth AG I RE 00845/04.07
Project 07: Check valve
Project/trainer information
If the flow in hydraulic system is to be blocked in one direction, a check valve is required.
Check valves are available as seat valves, with ball or poppet as closing element. They are subdivided as follows:
Check valves, pilot operated check valves.
Through the installation of a check valve it is possible to prevent, for example, the load pressure from driving a hydraulic pump reversely when the electric motor is switched off. Also pressure peaks, e.g. upstream of filters or coolers, can be reduced by means of a check valve installed in a by-pass.
However, the use of a check valve also results in additional resistance in the system so that a greater power must be installed.
The following Project 07 can be used to impart knowledge of the operating principle and the use of a check valve.
In the course of the project order the trainee is to understand the operating principle of a check valve installed in a by-pass. Through this project tasks he/she is to recognize the following:
• Fluid can only flow through a check valve in one direction.
• A check valve results in additional hydraulic resistance in the system.
• Pressure peaks can be reduced with the help of a check valve installed in a by-pass.
• When loads are secured by a check valve on the piston rod side, there is a risk of pressure intensification.
On the basis of the control set up on the training system the trainee is to understand the oper-ating principle of a check valve. A hydraulic cylinder under load, which is secured by a check valve, can be lowered by operating a shut-off valve. The cylinder velocity can be adjusted by means of a throttle.
To provide protection against pressure intensification a pressure relief valve is to be installed on the piston rod side.
Notes on detailed technical information about the check valve:
• The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 10
• Technical data sheet RE 20375 Check valve
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Project definition
In a fixture, a load suspended on a vertical cylinder is to be held by means of a check valve.
Lowering of the load should be possible with a shut-off valve. The piston rod side is to be pro-tected by means of a pressure relief valve. (The lowering movement via the electrical control is not an integral part of the order). The velocity is to be adjustable.
In order that the customer can understand your proposed solution, he requires technical docu-mentation.
In addition, he wants to know whether particular problems could arise, if a check valve is installed on the piston rod side.
Fig. 07.1 Practical example: Check valve
Project tasks
• Independent understanding of the task and its putting into practice using hydraulic control technology
• Planning and organizing the customer requirement (core qualification)
• Analyzing the technical data sheet of a check valve (specialist qualification)
• Handling of hydraulic components in line with functional needs
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Project 07:
Check valve Bosch Rexroth AG I RE 00845/04.07
Project steps
• Informing: Accepting and understanding the order, among others, through discussions with the customer.
• Planning: Planning and organizing the execution of the customer order; among oth-ers, through the selection of hydraulic components from the data sheet collection (RE 20375 Check valve).
• Deciding: Preparation of a schematic diagram sketch and selection of components.
• Executing: Set-up of the hydraulic control on the training system. Working out and documenting the system parameters requred by the customer.
• Checking: Are all customer requirements met?
• Evaluating: Are there further possibilities of meeting the customer requirement or simpler ways of project execution? Have unforeseeable problems occurred?
Notes
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Hydraulic circuit diagram
Fig. 07.2 Hydraulic circuit diagram: Control of a vertical cylinder with suspended load
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Item 1.1
Item 1.2
Item 1.0
Measuring glass
Power unit limit Item 0.1
Item 1.5
Item 1.3 Item 0.2
Item 0.3
Item 1.6
Item 1.4
5 Project 07:
Check valve Bosch Rexroth AG I RE 00845/04.07
Electrical circuit diagram
Fig. 07.3 Wiring diagram re hydraulic circuit diagram 07.2
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Retraction -Single-rod cylinder-Control 4/ directional valve
* Solenoid Y.b is not energized (Emergency stop)
Stop
Component selection with parts list
Item Qty Component designation Type designation Symbol
1.0 1 Double-acting cylinder
with single-sided piston rod with
load ZY 1.Last
1.1 1
4/3 directional valve with direct actuation by two solenoids, spring centering of the central position and central position P, A - B - T
DW 10E
1.2/1.5 2 Direct operated pressure relief valve, the cracking pressure can be
adjusted by means of a spring DD 1.1
1.3 1
Check valve with spring, flow possible in only one direction, rest position closed, cracking pressure 1 bar
DS 2.1
1.4 1 Shut-off valve, actuated by turning DZ 2.1
1.6 1 Throttle valve, adjustable DF 1.2
3 Distributor plate with four ports DZ 4.1
0.1 - 0.3 3 Pressure gauge with hose and quick release coupling
without check valve DZ 1.4
3 Hose with quick release coupling
with check valve DZ 25
Hose VSK 1
Table 07.1 Parts list for hydraulic circuit diagram Fig. 07.2
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7 Project 07:
Check valve Bosch Rexroth AG I RE 00845/04.07
Component arrangement
Fig. 07.4 Recommended component arrangement with component designation for parts list Table 07.1 and hydraulic circuit diagram Fig. 07.2
Note:
The designations of components in the parts list and the component arrangement are Rexroth-specific designations. Also the grid arrangement is Rexroth-Rexroth-specific and adapted for use on the training system.
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D Note:
In the case of connection elements marked with “D”, the components can be connected directly with each other.
Connection block Measuring glass
Set up the control as described below:
1. Mount the components required according to Table 07.1 in a clearly arranged form on the training system according to the prepared circuit diagram.
Connect the hydraulic control according to hydraulic circuit diagram Fig. 07.2 by means of hoses.
For connections, to which pressure gauges with minimess line DZ .4 are to be connected, use hydraulic hoses DZ 25. Hand-tighten the pressure gauge measuring lines at the relevant minimess connection of the hydraulic hose.
The correct and proper fit of the component connections with hoses can be checked by slightly turning the hoses.
Make sure that all ports - in this case also minimess lines - pipes and hoses are connected or that the ports are blocked with plug screws or protective caps. Leakage oil can drop through open ports on the floor and cause a risk of slipping.
Before commissioning the hydraulic control, i.e. before switching the hydrau-lic pump on, check, whether all pressure control valves are set to minimum pressure (spring unloaded) and all throttle valves are open.
Wire the electrical control according to wiring diagram Fig. 07.3.
Observe the installation direction of check valve Item ..
2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure.
3. Set the system pressure on pressure relief valve Item . to 50 bar plus one turn (in pressure line M).
Execution of the order Safety notes
To ensure the operability of plant and machinery, and consequently to allow the recognition of potential risks, safety regulations must be observed before and during the execution of the order. Relevant sources of regulations are given in the introduction of the present manual.
If work on electrohydraulic components is carried out improperly, risks of injury and a safety risk can arise during operation of the system, including danger to life.
Before starting work on the training stand, check that the electrical ON/
OFF switch on the hydraulic power unit is pressed in, i.e. that the system is switched off. Use the system pressure gauges to check that the system is depressurized.
Hydraulic systems can store pressure energy when at rest. It can cause injury when the system is opened.
Warning
Project 07:
Check valve Bosch Rexroth AG I RE 00845/04.07
4. By actuating push-button S solenoid Ya of 4/3 directional valve Item . is energized, i.e. the cylinder retracts. Opening of shut-off valve Item .4 causes the cylinder to extend.
5. Safety valve setting against pressure intensification on the piston rod side:
Starting position of the cylinder: B.D.C. (bottom dead center, cylinder extended).
Close shut-off valve Item .4. Set pressure relief valve Item .5 on the piston rod side to maximum pressure (spring tensioned - 1 turn).
Move the cylinder to the U.D.C. by operating push-button S. Move directional valve Item
. by manual operation to position Yb while opening pressure relief valve Item .5 on the piston rod side until pressure gauge M indicates a pressure of 80 bar (safety setting against pressure intensification on the piston rod side).
Check the set value by extending the cylinder again.
6. Check lowering of the load in the de-energized condition by opening shut-off valve Item .4.
The lowering velocity can be adjusted by means of throttle valve Item .6.
The pressure that builds up when the cylinder supports on the counterforce of pressure relief valve Item .5 on the piston rod side is called load holding pressure. To determine the load holding pressure, the cylinder must be at the U.D.C. While the shut-off valve is closed, slowly open the pressure relief valve until the cylinder starts to lower. M indicates the load holding pressure. On the basis of the load holding pressure and the dimensions of the hydraulic cylinder the weight of the load can be calculated.
Note:
To prevent pressure intensification, a safety valve (pressure relief valve) is used in practi-cal applications, e.g. in a welding fixture. The upward stroke is accomplished via a check valve installed in parallel.
After having completed practical work on the training system switch the hydraulic pump off! Set the throttle valve and the pressure relief valves to minimum pressure. For the disassembly, the load must be lowered. No pres-sure gauge may indicate a prespres-sure!
Evaluating the work results with regard to the customer requirement
• Fluid can flow through a check valve only in one direction.
• Load securing by means of a check valve on the piston rod side involves the risk of pressure intensification.
• The installation of a check valve results in the build-up of additional resistance in the direc-tion of flow.
• A check valve can be used as safety valve, e.g. to provide protection against pressure peaks.
Caution
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Notes
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