Jack Johnson, P.E.

Jack
L.
Johnson, P.E.
IDAS Engineering Inc.

Jack Johnson is an electrohydraulic specialist, fluid power engineering consultant, and president of IDAS Engineering Inc., Milwaukee. Contact him at jack@idaseng.com, phone (414) 236-5350, or visit www.idaseng.com.

Articles
Q&A about hydraulic servo and proportional valves
Got questions? So do we, but we also have answers. Electrohydraulic expert Jack L. Johnson, P. E., fields some of the recurring questions he encounters in his many educational sessions about closed-loop electrohydraulic control.
Manufacturing is still alive in the USA
A recent news item I heard on the radio announced that China will surpass the U. S. as the largest manufacturing nation in the world some time next year. If the general broadcast media are your primary source of news, you’re probably surprised that the ...
Case drain issues with pumps and motors
By Jack L. Johnson, P. E. Analytical schematics of pump and motor models were introduced in an earlier edition of “Motion Control.” Four different levels of models exist, arbitrarily numbered as Type 0 through Type 3, each one progressively more complex ...
Another look at pressure-reducing, pressure-compensated flow control valves
By Jack L. Johnson, P. E. Before concluding the discussion from last month, it will be helpful to review the equation for flow force because it begins to exert its effects on the valve performance any time pressure exceeds zero. Here is one of ...
Examining pressure-reducing, pressure-compensated flow control valves
By Jack L. Johnson, P. E. A pressure reducing, pressure compensated flow control valve is shown in a cartridge configuration in Figure 1. However, it is also manufactured in a conventional spool configuration. The operating principles are the same in ...
Understanding the unloading compensator, part 2
Summarizing last month’s discussion, Figure 1 serves as a starting point for explaining the test method used by manufacturers and users of unloading compensator valves and for the development of its math model. The basic test parameters are the 4-way ...
Understanding the unloading compensator
An unloading compensator is used with a fixed displacement pump to emulate a variable-displacement pump with load sensing — inefficiency notwithstanding.
Understanding unloading valves — Part 2
By Jack L. Johnson, P. E. To conclude our discussion of unloading valves, consider that Figure 5 adds a 4-way spool to the valve drawing of Figure 3 from last month. Note that the spool has two additional ports. They switch the sense line so that the ...
Understanding unloading valves — Part 1
By Jack L. Johnson, P. E. The last several editions of “Motion Control” explored open-center valve design concepts and showed that the term open center is considered as a misnomer by some observers. This is because the 4-way lands are often ...
Understanding parallel connected valves
In the past few editions of “Motion Control,” two types of open center valves were covered: the full series connection and the partial series connection. In this issue we’ll look at the third and final configuration: the parallel connection. ...
Load interactions in the full series system
Figure 1. The cutaway diagram shows that it is only the bypass flow from upstream functions that go to power the downstream functions. In continuing the discussion from last month, the partial series connection derives its name ...
Load interactions in the full series system
The last edition of “Motion Control” dealt with drawings to help visualize valve function in different ways. Toward that end, an additional variation of the analytical schematic diagram can shed light on the vast number of combinations that ...
Open-center valves in mobile equipment - Part 2
By Jack L. Johnson, P. E. Standard schematic drawings provide useful construction details of hydraulic circuits and complete systems, but they do not convey even the slightest insight into proportionality. A more descriptive representation ...
Open-center valves in mobile equipment
Most of the topics in this column have focused on industrial, or stationary applications. These machines usually feature some form of closedloop control, which requires continuous feedback of position, pressure or both. Mobile equipment, ...
Modeling the hydraulic pump
This scematic represents a second-degree pump/ motor model. The main component on the left side, representing mechanical apsects fof the pump/motor, is an idealized torque generator. On the right ...
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