Author Archive: Dzyanis

Schlumberger mast CTU at the tests

Dzyanis January 29, 2020 0 Articles 257 Views

Schlumberger mast CTUs at the tests

25 years ago I made one of the major decisions in my life – selected a specialty in the University. I remember my questions to one of the teachers of hydraulic and pneumatic systems faculty department: how long fluid power systems will be in demand for machines and different equipment? What is the chance I can find a job as a hydraulic specialist in 20, 30 years?…

Oh yes, that was a time when computers and electronics start to go by huge steps and I thought in a close future all hydraulic systems will be replaced with electric/servo drives.

Now, 25 years later, knowing the benefits of hydraulic systems and areas where fluid power solutions can be used more efficiently, knowing the modern trends and system design evolution, I can respond to myself: at least the next half of the century most power machines still will use a hydraulic system with a demand for specialists in this area.

Take a look at the picture – two more CTUs at our backyard during the test today. It is very impressive how the hydraulic system drives all equipment. How easy to design units like this with hydraulics! And how more complicated, expensive and less reliable this unit will be without hydraulics!

Our customer will get these units in work at soon. Well done!

Parker 689B series valve obsoleted

Dzyanis January 24, 2020 1 Articles Parker, valve 507 Views

Parker 689B series valve

So, Parker continues to discontinue nice products 🙂

Now they obsoleted valves 689B series…

It is hard to find panel-mounted hydraulic push button valves. Most of the push-button valves are cartridges and to be assembled with a body. Body has mounting holes and some design of brackets is required to mount to assy body + cartridge to the panel.

The benefit of the valve 689B series was in mounting holes at the top, which lets easy mount to the panel.

In most applications, I easily replaced this type with an electrical button that operates a simple solenoids valve. But some specific applications require simple hydraulic manual control (some equipment at the rig, where the electrical-over-hydraulic control is not allowed by safety reasons.)

So, the question to you guys, can you advise an elegant replacement for this valve?

Updates:

Jan 29, 2020 By the advice of couple vendors I ‘m going to try to use Doering push-button valve as a replacement:

Doering push-button valve

Different spacers can be used, but I’m going to proceed with custom spacers to make button hight as low as possible over the panel. Not really elegant solution but time is limited and I need to make a decision. I will update this pose as soon as the panel is done to show how the solution looks like.

Rexroth A4VG clones

Dzyanis December 10, 2019 0 Articles Parker, pump, Rexroth 459 Views

Just in case if you need replacement for Rexroth A4VG, it seems to me these guys are brothers:

Available Displacements:

Rexroth A4VG	Parker C-series	Dana Brevini S6CV
28cc, 40cc, 56cc, 71cc, 90cc, 125cc	55cc, 81cc, 136cc	75cc, 128cc
Nominal pressure:
400 bar (5800 psi)	420 bar (6090 psi)	400 bar (5800 psi)
Maximum Permissible Fluid Cleanliness:
20/18/15	20/18/15	20/18/15
Operating temperature:
−25..+110 °C	-25..90 °C	-25..90 °C
Viscosity range at operating temperature:
16..36 cSt	15..40 cSt	15..40 cSt
Available control systems:
“HD” Proportional control, hydraulic	“C” Hydraulic proportional control with internal feedback	“HIR” Hydraulic proportional with feed-back
“EP” Proportional control, electric	“F” Electric proportional with internal feedback	“HER” Electric proportional with feed-back
“ET” Electric control, direct operated, two pressure reducing valves	“G” Electric proportional without internal feedback	“HEN” Electric proportional without feed-back
“EZ” Two-point control, electric	“E” Electric non proportional	“HE2” Electric on-off
“DG” Hydraulic control, direct operated	“D” Hydraulic proportional control without internal feedback	“HIN” Hydraulic proportional without feed-back
– – –	“A” Manual lever	“HLR” Manual lever with feed-back

Semi-closed hydraulic circuits

Dzyanis November 28, 2019 0 Articles close loop, open loop, pump, Rexroth 1353 Views

Have you ever heard about the semi-closed hydraulic circuit?

The idea is to use open loop pumps in closed loop circuit. In the latest eighties, Mannesmann Rexroth (yes, that time Mannesmann yet!) even offered pumps A4VSH, especially designed for semi-closed circuits.

Bosch Rexroth A4VSH pump, from catalog RE92110/01.89

The main difference between closed loop pumps and semi-closed loop pumps was in addition block mounted to the ports A and B with check valves which let to supply suction flow from the tank, while mainstream comes from the motor to pump’s suction port:

Since that time Rexroth still builds A4VSH, but there are a limited number of sizes and options available and its no longer a mainstream published option.

But to make a semi-closed loop you do not need some special pump, it’s really easy to turn most standard open loop pump into a semi-closed loop circuit. Of course, you have to have some knowledge about the application and actuators before trying to apply it. If the pump does not have an integrated boost pump and check valves these are commonly added via an external gear pump and external check valves.

Here is the simplest example of the semi-closed circuit schematic where a regular open loop pump with LS control is involved to run two motors with independent proportional control of their speeds:
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