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
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 ...
Why mathematical models?
If you have been observing from the fringes, you may feel that mathematical modeling is rocket science. It isn’t — or, at least, it doesn’t have to be. A math model is simply an equation, or set of equations, that defines the physical ...
A Proposal for Hydraulic Pump and Motor Models
By Jack L. Johnson, P.E. All of us have probably used the equation that relates the output flow of a pump to its displacement (volume per revolution) and the input shaft speed (rpm): Q = (D N) 60 and that calculates the input torque to a ...
Myth #9: Servo and proportional valves can control no more than their rated flow
Servo and proportional valves are being used increasingly in critical applications in all technical areas — marine, aerospace, industrial, and mobile. The reason is simple: They offer a superb control. One of the perceived drawbacks, however, ...
Myth #8: Cylinders stop because the valve shuts off flow
Like so many of the myths and misconceptions surrounding hydraulic fluid power, the idea that valves are used to turn on and shut off flow is widespread. But, alas, in many cases it is wrong. The reason is simple: In spool valves, a physical ...
Myth #7: High Quality Must Sacrifice Quantity
Historically, management and engineering viewed issues of high production quantity and high quality as diametrically opposed. This double-Q dilemma maintains that if product quality is paramount, then production rates ...
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