Calgary, Alberta, Canada dzyanis@engineer.com

Fluid Power Pro

System Design

Articles around Fluid Power

Reliable close loop motor manifold

Just a note about one direction motors (not reverse!) in close loop applications.

There are a lot of different ways how to proceed with a hyd. motor in close loop applications to make motor work safe and reliable. From my experience, almost each one direction motor application is required to have the next items:

  1. Anti-cavitation check valve
  2. Pressure relief valve
  3. Case flushing valve
  4. Test ports

Each motor manufacturer has own solutions for their motors, but here are problems you can meet:

  1. OEM solution usually is not flexible: you can use only what they have. If you need for example flushing of the motor case – you have to design something external anyways.
  2. Price for these options is unreasonably high;
  3. Delivery time increased on 2..6 weeks;

Here is how I like to proceed for one direction motors – with an external manifold, mounted by hoses flange botls directly to both motor ports:

Motor Flushing

  1. The manifold is designed with through “A” and “B” SAE Code 62 ports with grooves for O-Rings from both sides. Using gender changer plates (for example, solution from Inserta) the manifold can be mounted in any direction/position and ports can be easy swapped if it required.
  2. Anti-cavitation valve is integrated to pressure relief valve is a very compact cartridge, which saves space in the manifold. Like an example, here are solutions from Hydac (DBRV16P) and Rexroth (MHDBN).
  3. Flushing flow control valves examples: HYDAC (SR06-01 or SR08-01) or SUN Hydraulics FDCB-LAN. The benefit of Hydac SR valves is SAE ORB cavity: if you do not need flushing valve you can still use this universal manifold but jut plug cavity with the regular ORB port plug.
  4. And of course test ports. I like to involve as many test ports as it is possible to make easy maintenance.

The benefit of using flushing flow control valve (vs fixed orifice) is: with flow control valve the flashing flow rate does not depend from charge pressure setting. I can be flexible with charge pressue setting for my system.

Flushing line from the manifold needs to be connected to the bottom case drain port of motor. From the top case drain port, the line needs to be plumbed directly to a tank.

Hydraulic cooler: suction or blowing air flow?

Just got an interesting response from Emmegi technical specialist about a choice between suction and blowing air flow of hydraulic coolers. The response is short but very deployed, so I would share it “as is”:

Here is our take on suction vs. blowing air flow:

  1. Blowing air flow: If you have seen a cooler that has been in the field for a while you will notice a clean doughnut shaped area where the air is blowing thru the cooler. In all four corners and in the center you will notice gunk/debris.

This indicates that the full surface area is not being utilized.

  1. Suction air flow: The fan creates a vacuum between the fan and cooling element. The air is very evenly distributed across the face of the cooler utilizing the full surface area.

On the downside, the fan blade is operating in less dense hot air, reducing the performance of the fan.

SUMMARY: For most hydraulic cooling applications the two effects cancel each other out and end up having nearly identical performance. The exception to this rule is for high temperature applications (oil temps above 175F).

  • For high temp applications the reduction of air density makes the blowing design more efficient.
  • The reason we supply standard coolers with suction air flow is that since the performance is typically the same, the suction air flow traps debris on the outside of the cooler where it is not only visible, but can be cleaned much easier.

if be honest, before this time I thought the suckers are more efficient coolers. Even to order cooler you need to specify symbol to make a blower (because the sucker is a standard).

Parker 50P filter will be discontinued soon

Just got a feedback from one of my Parker suppliers about 50P series filters: this series will be discontinued soon. I used them in a lot of my projects in the past and still continue to use them now. The supplier informed me about the next:

  • These filters are a pretty old design, from middle 1960’s and this is why this is a time to stop using these filters.
  • The suggested replacement for new projects (by pressure and flow rate) is WPF series
  • The price for 50P filters will be increased soon to stimulate customers to start to use WPF.
  • No more expedite option even with the price increasing for 50P filters.

The main problem with WPF filters is a design: Base-ported (50P) vs head-up (WPF):

Parker 50P vs WPF filters

In some applications where I use 50P filters now, will not be so easy to replace filters with new WPF series. There are a lot of factors like access to replace filter element in the current place, different mounting brackets will be required, extra hours for our mechanical engineers to design these brackets and etc.

Moreover, in the applications, we have already done for the years this replacement will not be possible at all.

This is why the best way if 100% replacement can be found.

Take a look at filter Schroeder KC50:

Schroeder KC50

  • Mounting dimensions are 100% the same (5″ x 4.5″):
    Parker 50P vs Schroeder KC50
  • Schroeder KC50 is approx. 2.5″ higher
  • The same rated pressure 3500 psi (240 bar)
  • The same flow rating: up to 100 GPM
  • BONUS: Filter elements are interchangeable!
    You can check Parker’s filter elements for 50P series here and you will be surprised: they matched Schroeder’s KC50 series!

So, if you take a look closer on Parker 50P and Schroeder KC50 you can find these products are 99% identical and we can use Parker’s filter elements in Schroeder filters and opposite.

Really, these filters are suspiciously similar! Therefore I made a request to Schroeder about KC50 filters and got a confirmation they were designed to be interchangeable. The only thing they noticed to be aware is the 50P had an option where they have a reverse flow check option for hydrostats in the housing and the Schroeder version of that filter assy is a KFH50. Also, for 3000 psi pressure (210 bar) you can save a little bit money and use identical filter KF30 series (with the same flow rate).

SANFAB Injector

What is a wonderful gadget I met today! Will try to use it in next applications. It used for oil recirculation, but it seems like you can make a close loop system with open loop pump, and get almost all benefits of the close loop:

  • reduced tank size
  • lower weight
  • higher pump work rpm

With benefits above this device is really welcome at the mobile applications where open loop pumps need to be involved. For example, at the project I’m working now, I got a situation where the open loop pump has to work at high 2500 rpm (2100 diesel engine + PTO ratio) and by some reasons open loop pump I need to use. And it isn’t easy to find not expensive open loop pump for so hight cont. work RPM.

If it is interesting here the link for the gadget: https://www.sunfab.com/products/accessories/injector/

Free Fluid Power Books

Fluid Power Basics

By this link you anybody can free download (or just read online) first couple chapters of “Fluid Power Basics” by Alan Hitchcox. This handbook is really just a basics and probably will be good enough for beginners. Unfortunately, full book is available for $59. But you always can read previous edition (from 2007) online by this link.

Pneumatics. Practical Guide

By clicking this link you can download very well illustrated eBook about pneumatic system design from Automation Direct. And it is really good book for beginners.

Electrohydraulic Control Systems

Here is a free eBook what I tried to use for proportional valve calculations. In the reality this book was not useful enough, but you can read it at least because it free for download. The book contains a lot of ads at the pages, so, probably, this is the reason why it free.

BASIC HYDRAULICS AND COMPONENTS

Very basics book for beginners from Yuken.

Hydraulic tank volume

The main rule for hydraulic tank sizing is: “bigger is better”, but because there is not always exist a possibility to find a lot of space for the tank (mostly in mobile applications) we need to know and follow min requirements for system calculation.

Just wanted to summarize all info I have for estimation of hydraulic tank volume:

Min. value Recommendation
Industrial application – Mineral Oil
2.5 times of all pumps flow + 10% for air cushion 3..5 times of all pumps flow + 10% for air cushion
Industrial application – HFC/HFD
5 times of all pumps flow + 10% for air cushion 8 times of all pumps flow + 10% for air cushion
Mobile application – Open loop pumps
1.5..2 times of all pumps flow + 10% for air cushion 2.5 times of all pumps flow + 10% for air cushion
Mobile application – Close loop pumps
1..2 times of all CHARGE pumps flow + 10% for air cushion 1.5..2 times of all pumps flow + 10% for air cushion

Please correct me if I’m wrong.