Electro-Hydraulic vs Hydraulic Component Reliability

[horsefeather]

The units I have operating (3000 psi/120 gpm) use hydraulic valves (proportion & directional)that are remotely piloted. I was going to build new equipment using the same configuration because I was not convinced that electrically controlled hydraulic valves were not as reliable. After talking with a respected Gulf Coast hydraulic expert, he assured me that the electro-hydraulic valves were every bit, if not more so, reliable as the remote hydraulically piloted type.

I'm reasonably familiar with the differences in cost and weight.

I'm reasoning that the added hydraulic circuits (remote pilot and valve pilot) increases my chances for contamination opportunity. The risk may be offset by an electrical actuator requiring an external interface seal and operation in a hostile environment.

Are there any opinions regarding reliabilty of the two designs in practical use?

 

[budt]

horsefeather wrote;

"The units I have operating (3000 psi/120 gpm) use hydraulic valves (proportion & directional)that are remotely piloted."

I understand this to mean you have Pilot Operated valves that operate the actuators and these pilot operated valves have Manual or Solenoid operated diectional control valves at another location with steel lines or hoses sending pilot oil to the pilot operated valves to control their position and the operation of the actuator they are attached to. The other option being pilot operated vaves that control the actuator with the solenoid control valve mounted directly to it with SHCS's.

The only problem I have witnessed with the remote arrangement is leakage due to more fittings and lines and increased sluggishness of the operation due to long pilot lines for the oil to travel thru. Also, Trouble shooting or Manual Operation can be a problem unless the solenoid valves are adequately marked so the correct function can be easily identified for manual override operation.

The up side of the remote setup is all the valve operators can be in a convenient location for maintenance instead of all over the machine. That is if the valves that power the actuators are located close to the actuator they are powering. Long flow lines to actuators also increases response time and adds to cycle time.

In my working area I only know of two circuits that use remote pilot operation and they are both over 50 years old. One is a 2500 Ton Hydraulic Press that has a 65 second cycle and has been in continuous operation since 1956.

The next time I design one with remote pilot operation will be the first one.

All the above is from my experience.



Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[horsefeather]

Of the 20+ controls in the cabin that control hydraulics none are electric (solenoid) operated. Aside from the directly operated selector (ball) and adjustment (needle) valves, there's usually a relief valve of some sort remotely piloting another valve. All the operator gauges that deal with high pressures are plumbed with deboosters to knock down the pressures.

As these rigs are used in oil fields, all hydraulic operations keep us away from those pesky spark source regulations.

The new plan is an all electric control cab directly operating the hydraulics. This will reduce weight, clean up the cab and, unfortunately, increase cost. My primary concern is reliability.

Incidentally the operators don't want the electric valves. I'm confident that I can provide a redundant power source and electric switches are extremely reliable when selected properly.

Thanks for the reply.

 

[MikeHalloran]

Electric switches are not reliable when operated with a hammer.

If the operators don't want electric controls, they will never work, no matter how you armor them.



Mike Halloran
Pembroke Pines, FL, USA

 

[budt]

horsefeather;

I'm not fmiliar with terms like "debooster" or have come across a relief valve operating a control valve, however I have never worked in the oil fields so that terminology may be standard. I have workid in the Coal Mining Industry a little and found the terms they use were different such as "Stinger" for what I call a Piston Rod.

After all that, are you familiar with Hydraulic Valves that are controlled with comprssed air? I have controlled several hydraulic circuits with Air Controls in explosive atmospheres and where the cylinders and valves were drenched with Coolant or Lubricating Fluid. These circuits had only short air flow paths for the ctrol air so they worked well. One machine air powered circuit I worked on had control lines of roughly 40 Ft. and the delay between the input or loss of signal was in the range of 5-10 seconds. Was not a problem in this case due to the machines function.

So, without more information I can't really be of much help with what you are trying to accomplish.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[horsefeather]

Deboosters are used to knock high hydrostatic pressures down to a reasonable value. Ours are 4:1 and are used for instrument readings and to keep high pressures out of the cabin. I don't think they are peculiar to the oilfield but my experience is limited. I have deboosters on some of my hydraulic, wellhead pressure and Cryo-Nitrogen circuits.

http://www.nov.com/Products.aspx?Pu...d=V3Q4IMLREFJI6GFOULWR8TMECNY=-AVGN1NIV1SE9OD

The hydraulic proportioning valves, various pressure control valves and my P12 pumps are remotely controlled by an array of pressure control valves and needle valves depending upon their purpose. It's not my design, I just take it as it was built. If electrically controlled hydraulic valves are as reliable as their remotely piloted brethren (subject of thread) I'm in the clear.

My cryo Nitrogen circuits are designed with pneumatic valves. It's been somewhat of an annoyance on my system diagrams reconciling nomenclature, reference designators and symbols for pneumatic, hydraulic and electronic components - but that's another forum.

Mike H's comments are taken seriously. Operator acceptance is proving to be my biggest resistance so far. Some of the other companies have built rigs with electronic controls with varying rates of success. I've somewhat mollified the operators with assurances that there is no computer involved in the control loop (yet) and automation is not a goal. There will always be an operator in the loop.

Thanks for the replies.

 

[budt]

horsefeathers;

I am bwing out of this thread since you are dealing with equipment I have never seen or heard of. My input would not be of any help since you are not using equipment that I have ever worked on.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[IceStationZebra]

Another major item to consider besides reliability is serviceability. By going electric over hydraulic you are causing a paradigm shift, and the operators and mechanics will NOT like it. Just remember what happened when computers appears on cars in the 80's. It will take twice as long to fix because the mechanic aren't proficient in electrical diagnosis. And I can guarantee that you will see perfectly good components replaced under warrenty because they didn't know what they are doing.

And owners think it is a money making scheme because either they need to invest in mechanic training or get the factory to support it. (not to mention special software or tools!)

If the benefits don't justify the trouble don't do it - being the innovator doesn't always pay.

ISZ

 

[EdDanzer]

Most excavators are still pilot operated, and as more electronic controls and sensors are added the reliability after 5 to 10 years of use continues to go down. The sensor wire connections tend to have water migration. One customer had to dry and grease the connections twice in 5 years on his 250 size excavator. High vibration and shock can cause wires to fatigue break and cause terminals to come loose.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[horsefeather]

Good points ICZ and EdD,

Oddly enough,I think I have a larger pool of electronic technicians to choose from than hydraulic techs. Other than my operator paradigm shifts I think I have the maintenance troubleshooting covered with good documentation, a good data acquistion system and some simple hydraulic skills training (reading pressures and flow). It may be easier to train an electronic tech to troubleshoot hydraulics than vice versa.

I hadn't considered the vibration aspect as contributing to reliability, but the truth of the matter is that the constant vibration in my systems probably keeps any contamination floating in the system from permanently lodging someplace - both in the pilot and valve spool. Unless specifically designed vibration is bad on electronics. I've just had got two actuators connected to my membrane Nitrogen generators that the screws backed out of. I'm sure the same thing can happen to my electro-hydraulic valves - particularly the after though solenoid valves. I'll pay attention to the vibration spec during parts selection.

Thank you

 

[hydtools]

horsefeather,
In addition to vibration tolerance of the components, consider the vibration tolerance of the installation and assembly of the wiring. Use stranded wire and solder the crimped connections for added security. Use lots of wire support to prevent wire movement, especially where wire goes into the valves and into the switches.

Ted

 

[budt]

horsefeather wrote;

"It may be easier to train an electronic tech to troubleshoot hydraulics than vice versa."

It's sad but true that most hydraulic or pneumatic trouble shooting is handled by Electrical types. They may not know how to fix the component they say is the problem but they can find the problem since they are trained in trouble shooting.

Unfortuanately there is little training in Hydraulics or Pneumatics and few in the Industrial world who have any idea how to trouble shoot a circuit. Fortuanately the circuits operate well past dirty oil, shake, rattle and roll conditions and abuse that would knock out other products that might be used as a replacement. Like the old ad for Timex, It takes a licking and keeps on Leaking. or was that Ticking?

I've been lobbying for trained, dedicated Fluid Power Engineers and Maintenence persons since 1980 with little success and a lot of grief from persons who think the system is too simple to need trained persons.



Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[horsefeather]

True words!

In my present little niche of the world, electronics hasn't penetrated yet so it's still intimidating to the hydraulic techs. Hence my simple electronic troubleshooting course.

I work with a fellow at another company that is a fountain of experience, not much on design and theory, but he has solved a number of assembly problems that the average tech would never solve. Anyway, because of the reduced parts count for hydraulics and its dependability this one fellow can direct the work of 8 other techs. If you have just one guy who has learned the system he is a multiplier. In the electronics world the sheer number of components and drawings imposes a higher level of troubleshooting competency and logical approach.

I interviewed a hydraulic vendor a couple of months ago and he questioned my requirement for a hydraulic diagram, this stuff was so simple he said diagrams weren't needed. Looking at my legacy equipment and that of my competitors he wasn't alone in his approach of no documentation. Maybe he's right, it keeps the cost down. Sometimes I wonder whether the people in the fluid engineering world are not their own worst enemy. I, for one, cannot give any thought to troubleshooting anything - gas/fluid/electrical without a schematic.

 

[IceStationZebra]

I have been blessed with an innate ability to troubleshoot and it has served me well in my 13 years as a professional off-highway test engineer and before. I had several electronics classes but very little formal hydraulic training. I am often bewildered that other people can't figure out simple problems like I can - but then I figure thats why I'm an engineer and they are not.

I also agree that "It may be easier to train an electronic tech to troubleshoot hydraulics than vice versa." You can't see electrons so you have to use tools to figure things out. Mechanics just tend to take things apart and look for the obvious - or worse yet just assume that the most complicated component is broken and replace it!

I also agree with Bud that there should be fluid power engineers. In my industry the "hydraulic engineer" is usually the a mechanical engineer who got stuck doing it, and from then on he is deemed the "expert". At my last job I was the only person who truly understood the electro-hydraulic system that was being used. About once a week I had to explain some nuance to the lead design engineer (and often more than once).

ISZ

 

[PNachtwey]

IceStationZebra (Mechanical) 4 Jan 08 21:30
Another major item to consider besides reliability is serviceability. By going electric over hydraulic you are causing a paradigm shift, and the operators and mechanics will NOT like it. Just remember what happened when computers appears on cars in the 80's. It will take twice as long to fix because the mechanic aren't proficient in electrical diagnosis.

How long does it take to learn how to use a multimeter? The multimeter lets the mechanic know if the valve is being activated correctly. To do the same with a hydraulically piloted valve the mechanic would need to have a pressure gauge and perhaps the best solution would be to have a pressure gauge permanently mounted for each hydraulically piloted valve. Even so there is no feed back as to wheter the valve spool has shifted without electric feedback. I don't think this is much of a maintenance issue. The hydraulically piloted valves would make it hard to monitor whether the valve is properly activated and I thought this was a major part of Horsefeather's application.

Since this is an oil field application, I see only one down side to electrically actuated valve and that is one must have explosion proof enclosures and the valves themselves must be explosion proof valves.

Since I deal only servo and servo grade proportional valves, I have a question for the rest of you that are more familiar with bang-bang valves. Are there bang-bang valves with spool feedback like there is for proportional valves? From a computer you can tell that the output of the computer is active. One can measure with a multimeter that there is a voltage or current but how does one know if the spool has moved if there isn't a feedback of some sort. This applies to hydraulically piloted valves too. If bang-bang valves don't provide feedback there will not be anything to monitor anyway. If there is then I would think that monitoring the spool position would be vital and that information would go back to the monitoring position. In this case the operator can monitor all the valves from operator's cab. This sure beat going out into the dangerous area of the oil rig and installing a pressure transducer every time a valve appears not to work.

If the benefits don't justify the trouble don't do it - being the innovator doesn't always pay.

This makes sense but think about this. Without electric feedback there is nothing to monitor. What is the Labview for? If one can monitor a oil rig from an operators cab it is also possible to monitor it from around the world now. That is one of the benefits of the 'monitoring' capabilities. If the system is all hydraulic then what do you monitor? What do you record?
It's the 21st century. I know some of the things that are being done in the oil field because our motion controllers are there. Yes, the operators and maintenance men are kicking and screaming about the new stuff they must learn but they also know that those that don't learn will lose in the end because of competition. There are also cases where remote handling of pipe is a safety issue. It is not only faster but safer to control the system by computer.

Electro-hydraulic valves are becoming more and more common in the oil field for doing pipe handling and for hydraulic lifts or pumping. I am NOT saying a proportional or servo valve is required but it would be nice to be able to monitor pressures and spool positions in a monitoring system. There is no way around it. There will be a need to learn how to use a multimeter.

 

[maytag]

I am in a steel mill environment-when industry deems equipment as "steel mill duty" it is for good reason. We have hundreds of electric-hydraulic valves (both bang-bang and prop)than are reliable. Our Komatsu railmount scrap handlers have some electric-hydraulic valves that give years of service. I have to agree with Peter that it would aid in troubleshooting and control to be able to moniter spool position. Just MHO from Arkansas, Maytag

 

[horsefeather]

Thank you Maytag for the information. Is there any particular brand of valve that you use?

PN wrote:

This makes sense but think about this. Without electric feedback there is nothing to monitor. What is the Labview for? If one can monitor a oil rig from an operators cab it is also possible to monitor it from around the world now. That is one of the benefits of the 'monitoring' capabilities. If the system is all hydraulic then what do you monitor? What do you record?

This particular application involves injecting steel tubing down an oil well (4-20K ft), and blowing gas and fluid mixtures into it. This causes sediment and other nasties to be ejected out of the well.

Monitoring in my application falls into two categories: Job monitoring which are the indicators that tell the operator how the job is going and system monitoring which are indicators that tell the operator/maintainors the performance of the system.

The operator looks at fluid pressure, wellhead pressure and amount of tubing in the hole. He looks at the hydraulic pressure indicators while operating the equipment and deduces the the nature of the well from changes in circuit hydraulic pressures based upon his experience, e.g. an increase in hydraulic pressure on the injector circuit indicates an obstruction in the hole.

The operator indicators are recorded on a paper chart recorder and, on some units, captured in an electronic data acquisition system. What gets captured, recorded and displayed is an ongoing topic that I am visiting some Canadian vendors for next week.

The Labview allows me to build my system and displays ahead of time using emulated sensor/effectors then drop the system in when the hydraulic vendor has it built.

I've kind of rambled off-topic here, I hope this may be of some marginal interest.

 

[maytag]

We use a lot of Bosch/Rexroth and Vickers. The high performance prop valves are generally Bosch/Rexroth or Moog. With the multimeter even a lowly mechanic such as myself can verify the supply voltage, output to the coil and with the spool position feedback option ,that the spool did indeed move-just another troubleshooting aid. Maytag

 

[ScottyUK]

We support a lot of Moog servo valves and have very few problems provided the fluid in the system is kept very clean. When fluid quality starts to slide we start seeing problems.

The most favoured tools we have are the multimeter as previously mentioned and a mA source which can directly drive the servo valve coil. We're able to use a COTS mA source - mine is a Fluke 715 - because of the specific electrical characteristics of our valves but a controllable current source is easy enough to come by if 20mA at about 10V is not enough. We don't have spool position feedback although this would be a godsend at the times when we are fault-finding.

The equipment is primarily looked after by the electrical & instrument technicians rather than mechanical, although the maintenance contract is administered by the mechanical guys. The instrument techs have little problem working with the hydraulics and are pretty good at fault diagnosis.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[horsefeather]

I know I've seen proportioning valves with electronic feedback, probably a LVDT with a sliding core but I suppose a linear pot could be used. I'm sure Rexroth has them ..... aah there it is in the Womack product catalog Model 4 WRE with feedback. It doesn't say whether the LVDT is ac or dc.

I'm content that if the electrical signals are correct and the hydraulic pressure is present go ahead and change out the hydraulic valve.

Most beginning techs have problems with solenoids (relays). If there are easy access points (terminal boards) to measure, with the device in circuit, it can be easy - +12 VDC on one side 0 on the other, must be the solenoid coil. Measurements on a removed plug are not as eay. The +12VDC is clear enough, determing that the other side is the desired ground and not an open is not as intuitive. Maybe I can build a breakout box. This is where simple applications of Ohm's law come in.

For current loop devices (4-20 ma), there's probably a clamp on gizmo that works with a meter, I can't give these guys an o'scope. Any recommendations?