Air, proactive maintenance for your hydraulic cylinders

Hello again Air,

In your last few hydraulic maintenance emails,
we've talked about repairing, testing and storing
hydraulic cylinders.

Today I want to explain some of the ways you can
increase the service life of your hydraulic cylinders.

A major cause of reduced service life is damage to the
surface of the cylinder rod. Dents and gouges in the
rod's hardchrome surface reduces the life of
the rod and wiper seals.

Not only that, it gives dust and other contaminants
an easy path into the hydraulic system, increasing
the load on the systems filters.

The potential for damage to cylinder rods and wiper seals
is an ever present problem - especially for users of mobile
hydraulic equipment.

One way to minimize this problem is to install a protective
shroud or bellows to any cylinders exposed to impact damage.
This helps protect the rod's surface from dings and scratches.
In abrasive or corrosive environments, it also helps extend
rod and wiper seal life and provides an extra barrier to the
ingression of contaminants via the cylinder rod.

That said, the use of a protective shroud is an ideal
that's not practical in all cases. So in your next
hydraulic maintenance email in a few days time, I'll
explain an alternative that offers similar
life extension benefits.

Yours for better hydraulics knowledge,

Brendan Casey
Author of 'Insider Secrets to Hydraulics'; and
'Preventing Hydraulic Failures'.
http://www.hydraulicsupermarket.com/books.html
=======================================

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HydraulicSupermarket.com
1195 Hay St
PO Box 1029
West Perth, US-WA 6872
Australia
6 (189) 380-6659

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Air, are your cylinders hoop stressed?

Hello again Air,

In your last hydraulic maintenance email,
I explained how to use volumetric efficiency
to correctly determine the condition of
a hydraulic pump.

Today I want to continue on this tack
and talk about testing hydraulic cylinders.

The conventional way of testing the integrity
of the piston seal in a double-acting cylinder
is to pressurize the cylinder at the end of stroke
and measure any leakage past the seal. This is
commonly referred to as "end-of-stroke bypass test"

The major limitation of the end-of-stroke bypass test,
is it generally doesn't reveal ballooning of
the cylinder tube caused by hoop stress as a result
of under designed cylinder wall thickness or reduction
of wall thickness through excessive honing.

The ideal way to test for ballooning of the cylinder tube
is to conduct a piston-seal bypass test mid-stroke.
The major difficulty with doing this is that the force
developed by the cylinder has to be mechanically resisted,
which in the case of large diameter, high-pressure cylinders
is impractical.

However a mid-stroke bypass test can be conducted
hydrostatically using the intensification effect.
The necessary circuit along with a step-by-step
procedure for conducting this test is shown at:
http://www.insidersecretstohydraulics.com/cylinder-testing.html

Yours for better hydraulics knowledge,

Brendan Casey
Author of 'Insider Secrets to Hydraulics'; and
'Preventing Hydraulic Failures'.
http://www.hydraulicsupermarket.com/books.html
=======================================

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provided by the 'Inside Hydraulics' newsletter
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HydraulicSupermarket.com
1195 Hay St
PO Box 1029
West Perth, US-WA 6872
Australia
6 (189) 380-6659

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A tragic story and a stark hydraulics lesson

Air,

Large hydraulic cylinders are real pigs to repair.

They're not complicated. Like any other cylinder,
you've got a rod, a tube, a gland, a set of seals
and some wear bands.

So long as all tolerances are correct,
there's no rocket science involved in carrying out
an effective repair.

But as anyone who has carried out repairs on long,
large diameter hydraulic cylinders knows,
they're pigs to get apart and back together again,
even when you've got all the right equipment
at your disposal.

Give me the choice of overhauling a large piston pump
or a large cylinder and I'll take the piston pump
any day of the week.

But for most mechanical types, the complexity
of a piston pump would scare them off.

Which means it must be the apparent simplicity
of large hydraulic cylinders that lures people
into attempting repairs on them - when they
don't have the necessary equipment to get them apart
and back together again - safely.

This can be real dangerous.

And a recipe for disaster, as this tragic story
sent to me by one of our members from Venezuela
illustrates:

"A maintenance supervisor and mechanic were trying
to extract the rod/gland assembly from a
large hydraulic cylinder.

In their attempt to do so, they pressurized the cylinder
with approximately 100 PSI (6.9 bar) of compressed air
with the objective of pushing the gland out.

This attempt failed. So they figured that, in addition
to applying force with compressed air, they could
apply heat around the circumference of the cylinder tube,
in the vicinity of the gland.

They thought that this would expand the tube and
release its grip on the gland assembly.
So they used an oxy-acetylene torch to apply heat
to the surface of the tube.

Within minutes, the gland assembly blew out
with a deafening explosion.

The air collected the residual oil in the cylinder
as it rapidly de-compressed. And the air/oil mixture
ignited into a fiery inferno when it contacted
the torch's open flame.

Both men were knocked to the ground by the force
of the explosion.

They were both covered in hydraulic oil
as it sprayed out of the open end of the cylinder tube
and they were both engulfed in fire.

A passer-by grabbed a fire extinguisher
and doused the flames. However, the force
of the heavy gland assembly ripped
the maintenance supervisor's leg off
as the explosion blasted it out of the cylinder.
He also suffered extensive burns.

The maintenance mechanic suffered extensive burns
and a broken leg."

The obvious lesson here is:
never use compressed air and/or heat
to extract the piston rod from a cylinder tube.

NEVER.

But the wider lesson is:
pick your battles wisely.

KNOW what you can and can NOT accomplish (safely)
with the knowledge, tools and equipment
available to you.

I always work on the assumption
that if you're reading my stuff,
you're over 18 years of age.

So as a grown-up, far be it for me
to tell you what you can and can not do.

Just don't get killed or maimed by ignorance.

Yours for better hydraulics knowledge,

Brendan Casey
www.hydraulicsupermarket.com/made-easy

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HydraulicSupermarket.com
1195 Hay St
PO Box 1029
West Perth, WA 6872
Australia
6 (189) 380-6659

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Air, time for a pump overhaul?

Hello again Air,

In your last hydraulic maintenance email,
we talked about how to avoid troubleshooting
mistakes by checking and eliminating
the easy things first.

Today I want to move onto how to determine
the condition of the hardest working component
of a hydraulic system - the pump.

As a pump wears in service, internal leakage increases
and therefore the percentage of flow available
to do useful work (volumetric efficiency) decreases.

If volumetric efficiency falls below a level considered
acceptable for the application, the pump will need
to be overhauled.

In a condition-based maintenance environment, the decision
to change-out the pump is often based on remaining
bearing life or deterioration in volumetric efficiency,
whichever occurs first.

Volumetric efficiency is the percentage of theoretical pump flow
available to do useful work. It is calculated by dividing
the pump's actual output in liters or gallons per minute by its
theoretical output, expressed as a percentage. Actual output
is determined using a flow-tester to load the pump and measure
its flow rate.

Because internal leakage increases as operating pressure
increases and fluid viscosity decreases, these variables
should be stated when stating volumetric efficiency.

For example, a hydraulic pump with a theoretical output
of 100 GPM, and an actual output of 94 GPM at 5000 PSI
and 120 SUS is said to have a volumetric efficiency
of 94% at 5000 PSI and 120 SUS.

When calculating the volumetric efficiency of
a variable displacement pump, internal leakage
must be expressed as a constant.

To understand why this is so, think of the various leakage paths
within a hydraulic pump as fixed orifices. The rate of flow
through an orifice is dependant on the diameter (and shape)
of the orifice, the pressure drop across it and fluid viscosity.
This means that if these variables remain constant, the rate
of internal leakage remains constant, independent of
the pump's displacement.

For a detailed example, which shows how costly it can be if
you don't understand this concept, read the rest of this story:
http://www.insidersecretstohydraulics.com/variable-hydraulic-pump.html

Yours for better hydraulics knowledge,

Brendan Casey
Author of 'Insider Secrets to Hydraulics'; and
'Preventing Hydraulic Failures'.
http://www.hydraulicsupermarket.com/books.html
=======================================

If you no longer wish to receive the valuable guidance
provided by the 'Inside Hydraulics' newsletter
and associated mailings, point your browser to this page:
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HydraulicSupermarket.com
1195 Hay St
PO Box 1029
West Perth, WA 6872
Australia
6 (189) 380-6659

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Air, a big tip on hydraulic troubleshooting

Hello again Air,

In your last hydraulic maintenance email, I explained
how to prepare your spare hydraulic cylinders
for long term storage - and how to do it safely.

Today I want to switch gears and talk about one of
my favorite subjects - hydraulic troubleshooting.

As I explain in my book 'Insider Secrets to Hydraulics',
hydraulic troubleshooting involves a lot of science and
a bit of art.

While there's no substitute for knowledge, the right tools
and experience, you can approach any troubleshooting situation
like a pro - just by starting with this one step:

Check and eliminate the easy things first.

Now, in case you're thinking this advice is too obvious
to be useful, consider this troubleshooting situation
I was involved in recently:

The machine in question had a complex hydraulic system,
the heart of which comprised two engines driving
ten hydraulic pumps. Six of the pumps were variable displacement
and four of these had electronic horsepower control.

The symptoms of the problem were slow cycle times in combination
with lug-down of the engines (loss of engine rpm). The machine
had just been fitted with a new set of pumps.

The diagnosis of the mechanic in charge was that the hydraulic
system was tuned above the power curve of the engines, that is
the hydraulics were demanding more power than the engines
could produce, resulting in lug-down and therefore,
slow cycle times.

The other possible explanation of course, was that the engines
were not producing their rated horsepower.

Due to the complexity of the hydraulic system, I knew that
it would take around four hours to run a complete system check
and tune-up. So in order to eliminate the easy things first,
when I arrived on site I inquired about the condition of
the engines and their service history.

The mechanic in charge not only assured me that the engines
were in top shape, he was adamant that this was
a "hydraulic" problem.

Four hours later, after running a complete check of the
hydraulic system without finding anything significant,
I was not totally surprised that the problem remained unchanged.

After a lengthy discussion, I managed to convince the mechanic
to change the fuel filters and air cleaner elements
on both engines.

This fixed the problem. It turned out that a bad batch of fuel
had caused premature clogging of the engine fuel filters, which
were preventing the engines from developing their
rated horsepower.

Had the relatively simple task of changing the engine fuel filters
had been carried out when the problem was first noticed,
an expensive service call and four hours of downtime
could have been avoided.

The moral of this story and troubleshooting lesson 101 is:

ALWAYS check and eliminate the easy things FIRST.

For more tips on troubleshooting hydraulic problems,
read Chapters 7-11 of 'Insider Secrets to Hydraulics'
http://www.hydraulicsupermarket.com/books.html

Yours for better hydraulics knowledge,

Brendan Casey
Author of 'Insider Secrets to Hydraulics'; and
'Preventing Hydraulic Failures'.
http://www.hydraulicsupermarket.com/books.html
=======================================

If you no longer wish to receive the valuable guidance
provided by the 'Inside Hydraulics' newsletter
and associated mailings, point your browser to this page:
https://hydraulics.infusionsoft.com/opt?o=2&i=123560&m=780222&e=c893403f

==========

HydraulicSupermarket.com
1195 Hay St
PO Box 1029
West Perth, WA 6872
Australia
6 (189) 380-6659

Delivered By Infusionsoft

Air, how to store hydraulic cylinders - safely

Hello again Air,

In your last hydraulic maintenance email, I wrote
about the importance of checking rod straightness
when repairing hydraulic cylinders.

Today I want to continue by talking about
how to prepare hydraulic cylinders for storage -
after they've been repaired.

Here's what I recommend if you're storing
spare hydraulic cylinders for an extended period:

1. Always store fully retracted.

2. Store indoors in a clean, dry area.

3. Smear the internal surfaces of eye/clevis bushes
or bearings with grease - particularly if they're steel.

4. Protect any exposed chrome on the rod. Oil-impregnated tape
such as Denso tape can be used for this purpose.
Before applying, make sure the rod is fully retracted.
If a product like Denso tape is applied to the rod when
the rod is not fully retracted, subsequent retraction
of the rod can result in damage to the rod seal.

5. Plug the service ports with steel - not plastic, plugs
or blanking plates.

6. Consider filling the cylinder with clean hydraulic oil
through its rod-end service port. Particularly if it's
an expensive, large diameter or high pressure cylinder.
I say "consider" because there are a few issues to understand
before you carry out step #6.

If the cylinder is not filled with oil it will obviously
be filled with air. If this air is not perfectly dry,
then as ambient temperature decreases the air
can reach dew point. This results in moisture forming
on the inside of the cylinder tube.

This can cause spot rusting and pitting of the tube surface,
which will reduce the volumetric efficiency of the cylinder,
the service life of the piston seal, and ultimately,
the life of the tube itself.

Completely filling the cylinder with clean hydraulic oil
prevents this from occurring, however there's
a MAJOR CAUTION with doing this. I don't have room
to explain it here, but I encourage you to read about online:
http://www.insidersecretstohydraulics.com/storing-hydraulic-cylinders.html

Yours for better hydraulics knowledge,

Brendan Casey
Author of 'Insider Secrets to Hydraulics'; and
'Preventing Hydraulic Failures'.
http://www.hydraulicsupermarket.com/books.html
=======================================

If you no longer wish to receive the valuable guidance
provided by the 'Inside Hydraulics' newsletter
and associated mailings, point your browser to this page:
https://hydraulics.infusionsoft.com/opt?o=2&i=123560&m=778496&e=c893403f

==========

HydraulicSupermarket.com
1195 Hay St
PO Box 1029
West Perth, WA 6872
Australia
6 (189) 380-6659

Delivered By Infusionsoft