Monitoring Hydraulic Systems

[horsefeather]

In an attempt to bring our equipment into the 20th century I'm designing an integrated monitoring system that is used when the equipment is operating. At this point it is only monitoring, the next phase will move into control.

Aside from the monitoring of case drain flow that brought me to this forum along with temperature and pressure, what other things should I be keeping an eye on?

My particular system uses a primary close looped component to operate specific hydraulic motors and an open loop component to operate auxilairy motors and cylinders. Anything peculiar to closed loop I should keep an eye on?

This, of course, would be over and above a fluid sampling program.

I've seen a particle counter that fits inline (Pirtek PC9000) that looks interesting.

 

[PNachtwey]

Anything peculiar to closed loop I should keep an eye on?

http://www.deltamotion.com/products/motion/

What is the application?
What brand and make of PLC are you using?

Peter Nachtwey
Delta Computer Systems, Inc.

 

[horsefeather]

My application involves snaking steel pipe down oil wells and blowing out the crap. The pipe handler and reels and numerous auxiliaries are hydraulically operated.

I'm considering National Instruments platforms. I'm not convinced that use of a PLC based architecture is relevant or even desirable anymore.

I see there is a PLC forum, maybe I'll discuss over there.

In the meantime, aside from low conductivity and high viscosity, are the any other properties of hydraulic fluid that provide a challenge in measurement that is different from say, waste water?

Or perhaps elements of a close looped system that should be monitored to ensure performanc?

 

[budt]

You should also be measuring Flow from Pumps Outlet and Case Drain and to and from all circuits. The base would be when the circuit is running as designed so any change in flow would be observed and shown. This would detect leaks, excess bypass due to wear, mis-applied operator intervention or ny other flow interuption.

There is a company that makes a Flow Meter that has probes in the flow lines a certain distance apart that measures the heat difference and can apply that info to the pipe size to determine flow. Never tried that system yet but if it works as stated it would not cause a lot of back pressure and should be long life.

One biggie in Closed Loop circuits is the condition of the oil in the closed loop. Often that oil is a lot more contaminated than the rest of the system and can knock out pumps and/or motors quickly. Especially after one of the units fail catastrophically.

The other one is the case flushing oil flow from the Replenishing (Charge) pump. Usually the Flushing Flow is routed through the Motors Relief Valves and back through the Pump Case. No matter how much the Pump or Motor are worn Case flow is always Replenishing (Charge) Pump flow.

If the pump and motor are bypassing 6 GPM each it means the 10 GPM Flushing Flow going into the low pressure side of the loop is not enough to keep it full and the pump is cavitating due to lack of oil. This would show up as a pressure drop in the low pressure side of the loop since it is asking for more oil than the Replenishing pump can provide. This would be evident at first when the circuit is at higher pressure and flows greater than Replenishing (Charge) pump flow.

At least that is my understanding of Closed Loop circuits.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[budt]

Here is a link to a themal mass flow meter.

http://www.flowmeters.com/ufm/index.cfm?task=thermal

Here is a link to all types of flow

http://controlsweekly.com/flow.htm#Thermal

Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[horsefeather]

I guess there are a couple points of view on closed loop systems. One would be the finite amount of trapped fluid getting progressively dirtier view or the finite fluid uncontaminated by the rest of the fluid in the system view. Both would be offset by charge pump replenishment. My particular application with the closed loop system has filters on both sides. My primary concern is contamination entering through the charge pump from the open loop reservoir. Also I'm not sure if the closed loop fluid will be cooled sufficiently as the cooling is on the open loop side, I've got the contract engineers looking into it.

In the meantime, my closed loop motors are limited by the manufacturer to 100 hp. I need to sense pressure and flow, perform the algorithm and turn on a warning light when the operator approaches the hp limit. I'll look into the thermal flow meters more closely. Thanks.

 

[dbaird]

I would think contamination control would be important. Check this article:

http://www.hydraulicspneumatics.com/200/Issue/Article/False/77226/Issue

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[kcj]

FWIW notes:
1. 'closed loop' is often confusing. Hydr people mean it to be closed circuit, i.e hydrostatic drive: oil from pump to motor to pump, not directly back to tank.
Peter's controls world 'closed loop' means command, monitor the results, than change the command via the feedback.

2. Even in closed loop hydrostatic, the oil does not stay in the loop long. If the charge pump is say 10 gpm and circuit volume is a few gallons, the oil is exchanged several times a minute. Larger drives, say 100 gpm charge flow and 50 gallons in the piping, same story.
This assumes the flushing valve is located properly in the circuit to do the exchanging. Circuits with charge relief only, no flushing valve, wuld indeed run the same oil round & round except for leakage.

3. I'd like to hear someones expereinces with the thermal type meters. That concept has been used on air flow/velocity meters for long time, would be great if works on oil.

kcj

 

[horsefeather]

kcj,

1. Closed circuit is correct. I'll modify my usage.

2. I suspect the oil turns over sufficiently. The replenishment circuit has a filter in it and fluid is drawn directly from the tank.

3. Any experience with flowmeters in an oil environment is welcome. My engineering background is electronics; book learning on fluid power can only get me so far.

Thanks for the correction.

 

[budt]

I specify Flow Meters fitted with Proximity Switches and set above typical drain flow on all Case Drains. This will catch pumps or motors that are deteriorating or oil that has degraded to the point of bypassing excessively due to thinning viscosity and can signal a problem before a pump comes apart.

I also specify Flow Meters on all Pump Outlets for Trouble Shooting. On these I use two 3-way Ball Valves and pipe them straight thru for normal flow and install the Flow Meter in a side loop for Trouble Shoting. It is more expensive up front but the Flow Meter is not deteriorating continuously and is in good shape when needed.

Take a look at the Fluid Power Ebooks at this web site to see what I use to teach Fluid Power Basics and an advanced Circuit Design class. It covers Hydralics primarily but also goes into Pneumatics where fluid compressibility can give different end results.

The crcuits book is 375 pages of all the circuits I have ever used or come across and shows the valves and actuators in the At Rest condition plus how they function to make the circuit perform. The facing page is an explanation of how the circuit works normally and some of the results of typical failure modes. You must be familiar with Fluid Power symbols and the hardware they represent to get mush out of this one. A prerequisite is the basic class or a good knowledge of symbols.

They are being put up a chapter every couple of weeks and the basic book is almost complete. The circuits book is just starting.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[horsefeather]

I'm sold on the value of case drain flowmeters, I'll probably usesomething from the Hedland product line.

I've got to build some mobile hydraulic power units (HPU) later this year and have been mulling the idea of an onboard flowmeter. If I build 10 units, that's 10 flowmeters; which sit idle unless a problem occurs. Plus that is one more valve that the operators can misconfigure. I've kind of settled on the maintenance tech traveling with a flowmeter.

I'm up on the symbols with an occasional reference to the vendor literature. The reference I've been using is Rohner's Industrial Hydraulic Control, a reasonably informative book except for its use of SI units.

I'll check out the e-book as soon as I locate the link.

 

[budt]

I just found out the web site did not show as entered. The books are at

http://www hydraulicspneumatics

com and look in the Ebooks link.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[hydtools]

Horsefeather, we used to build portable power units with flow meters and pressure gages. We stopped doing that. The gages and meters confused the customer in that he misinterpreted the information and we would receive calls for problems that did not exist. The pressure gages would eventually fail. The gages and meters were not worth the cost to have them on the power units.

We found that a portable flow and pressure tester with the tech was the better way to go. All the troubleshooting could be done with it.

Ted

 

[budt]

Ted wrote;

"The gages and meters confused the customer in that he misinterpreted the information"

It was probably more like they had no idea what they were looking at and how to interpret the information since most Maintenance and Engineering persons have little or no training in Fluid Power systems.

I believe the same person would have the same problem with an Ammeter on an electrical circuit if there was no EE or Electrical Maintenance person on site to guide them.

I always specify "Push to Read" Gauge Isolators, that vent oil to Tank when released, on all Pressure Gauges since there is absolutely no reason for them to be operating continuously. With a Gauge Isolator in stalled the Gauge mechanism is in as new condition when a pressure test is required unless it has been physically damaged and not replaced.

An even better solution for Pressure Reading is a central gauge station with one Gauge and a Selector to read all the areas a Pressure gauge would normally be installed. The gauge is isolated until pressing on the selector and since the same gauge is used for all test's there is no danger of having a bad gauge for one or more of the test points. If the Gauge is off it is off the same amount for all readings.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[horsefeather]

Thanks Ted and Bud,

My customers are operators who, frankly, are not expected to know anything about fluid power or repair the equipment. It's complicated enough snaking steel tubing into wells and servicing them. The gauges that are used only aid in operations. Any diagnostic equipment provided would serve only to aid the maintenance techs. Simple things like case drain flowmeters will be checked by operators during pre-op in the yard and during operations with the Data Acquistion System (DAS) illuminating a light and warning that something was amiss.

My nitrogen generation units have a central gauge station for diagnostics that works well; but it's all digital with tansducers. When a problem is encountered the tech asks for the operator to step through the selector and read out the values over the phone. Some of the more savvy operators understand the circuits and can provide an idea of what's wrong.

I'll start another thread on the HPU when I get started on the design.

 

[kcj]

BUD
Where do you get the gauge isolators?
LHA or Gits or someone had a selector version years back, but I have had use for single gauge, 3 ported isolators. I find the two ported ones, block only, no venting to tank.

So any sources of venting or blocking type isolators will be helpful.

kcj

 

[hydtools]

kcj,
Here's one:

http://www.lenzinc.com/index.cfm?template=catalog&form_product=174

Ted

 

[budt]

Kevin;

I tried to send some links a short time back but see they did'nt get on for some reason.

The one Ted posted is good.

I found LHA has been sold to Donaldson but there site shows no Gauge Isolators.

Others that look good are:

http://www.stauff.co.uk/Portals/3/PDF Cats/Accessories/06_Pressure_Gauges.pdf

http://www.parker.com/euro_hcd/new_web_page/pdf_2500uk/wm1.pdf

http://www.magnaloy.com/Products/fluid_power_accessories/gauge_isolators.htm

Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[kcj]

Perfect, tks all.

Used Lenz o-ring flareless tube ftgs for years, Stauff gauge quick couplers and magnally shaft couplings are my preferred choices respectively. never knew any of them had the isolators.

What, LHA about the only company that didn't get bought by Parker!

kcj

 

[IDesignHyd]

http://www.DMIC.com

They have turn to read gauge isolators.