Hydraulic design is like a day's fishing

When I was a small boy, nothing was more exciting than going for a day’s fishing. Not that I can remember catching much but it was the anticipation that it might just be the day when I would catch a whopper!
Many years later I now see how the experts do it and it is hardly surprising I caught very little. As a child I used the same method of fishing regardless of the conditions, location or the type of quarry I hoped to land.  Top fishermen plan their task and select the right equipment to suit the conditions.
If they get it wrong, at best they will catch very little and at worse loose or break their equipment because the fish was too large for the tackle they selected for the task.
Now let us consider the Hydraulic designer, he must also consider the task. What are the loads and speeds required?  Where will the equipment be used, (hot, cold, wet or dirty) and from a basket of pumps, valves, actuators and controls, select the right parts for the best result. Get the selection wrong, at best will not achieve the task and at worse cause significant damage to your customers equipment. Get it right and it’s as satisfying as catching the Whopper!
Good fishing.
Bob
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Hydraulic pump suction strainers

I return to an old subject, should we fit pump suction strainers?
I posed this question to my Linked in forum (Hydraulic help) and the overwhelming opinion was to leave them off.
For those just starting out in hydraulics let me briefly recap on the purpose of suction strainers.
As its name implies this is not a typical filter but simply a piece of 125micron metal gauze rolled into a tube that fits to the end of the pump suction pipe. Particles over 125 micron will be blocked thus preventing them entering the pump possibly causing instant destruction. This sounds very admirable and because of their low cost one would see no reason for not installing them, however there is a downside.If the suction line is restricted Hydraulic Pumps will quickly deteriate due to cavitation. 
Suction strainers can be difficult to change and most often end users are totally unaware that they even exist. Over time this will result in the gauze silting up and blocking the oil flow to the pump and may even collapse the strainer with catastrophic results.
Many engineers say that if the tank is very clean and free of all weld splatter, the strainer will serve little purpose.  This strategy however is not risk free because you must be 100% sure that there is no way that any contaminant can drop into the tank, that the paint inside will not flake or peel and that hoses and pipework have been thoroughly cleaned prior to start up.
My opinion is, look at the application and risk assess the environment, housekeeping abilities and responsibilities of the user and the implications of serious pump failure with the consequence of serious contamination throughout the system and potential downtime to the plant. Also talk to your customer about these issues.
keep safe
Bob Jackson
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Hydraulic Hose Burst Valves

Hydraulic Hose Burst Valves
I have talked many times about my dislike for Hose Burst valves (velocity fuse).
A cheap and nasty little valve that screws directly into the cylinder port and should close when the velocity across the valve exceeds the spring setting.
So why do I hate this valve so much?
Many unwitting users do not realise that these valves must be properly adjusted using feeler gauges if they have any chance of them working properly. The manufacturer should supply a chart with the valve showing a valve gap dimension based on flow. This is not the flow of the pump but the flow that will pass from the cylinder under normal conditions and is calculated using the displacement volume of the ram and its velocity.
The valve will not compensate for any change in temperature or load and can often close when operating under normal conditions, causing annoying stoppages. However the main purpose is that they must close should a pipe or hose burst. If the worst happens and the valve does not close, the result can be catastrophic and cause serious damage or injury.
If you are serious about protecting against hose burst then spend a little more money and do the job properly using a Pilot Operated Check valve. It will react instantly and must be built in as part of the cylinder with no pipe between the cylinder port and valve except for the pilot. This is a better quality valve and much more reliable.
Always keep in mind that there is NO complete failsafe way of hydraulically holding up any load with a ram except by using mechanical locking. Even if a new installation initially holds well, time and wear will eventually increase leakage and the load will creep down.
Be safe.
Bob Jackson (The Hydraulicman)
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Dangerous Cranes

I think most will agree that hydraulic crane safety should be of paramount importance and I would like to mention just a few observations about the use of this potentially dangerous piece of machinery.
In my opinion the safest type of crane has been designed to prevent overloading. Not just on the main lift but more importantly where you pick up a load and then telescope out. As the telescope extends increasing its length the main lift cylinder pressure also increases in proportion.
Now some cranes have load sensing devices that will disengage the telescope so that overloading cannot occur and stop the telescope extending when the maximum load is exceeded.
Also the counterbalance valve can also relieve and lower the load in a controlled way.
However there are some cranes that I have come across where they have been fitted with a simple hand valve with all blocked centre ports. These cranes have often been salvaged and the hydraulics replaced by people not proficient in hydraulic systems or crane design. Unwittingly the users of these cranes are just waiting for disaster to strike, at best causing costly damage and at worst serious injury.

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very best
Bob

Hydraulic Circuit Conventions

Fault finding hydraulic systems can be difficult but much harder without the benefit of an accurate circuit diagram.
Many systems are very simple, a pump, relief and directional control valve. This is straight forward and easy to follow but more complex systems with large manifolds can be almost impossible without the benefit of a circuit.
To the un- initiated eye, circuit diagrams can look like something written by a creature from a distant planet but circuit diagrams and symbols are quite easy to understand.
I always say to students that hydraulic symbols are similar to road signs and will resemble the components it represents. (a spring looks like a spring, a flow path an arrow)
What I find irritating and most annoying is when I pick up a circuit drawing that has come from a well known International hydraulic company that have symbols I do not recognise or maybe a Relief valve drawn instead of a Reducing valve. I even see symbols that have been made up, created and nothing I have ever seen in ISO or CETOP standards.
Many of us would not be particularly fazed by a Relief Valve being misplaced by a Reducer because of it’s the location in the circuit. but on my complex circuits, non standard symbols can be confusing and result in a lot of head scratching and wasted time.
Like any engineering drawing, circuit drawings should be clear, unambiguous and follow proper International standards. If we all start designing own symbols and drawing circuits without proper convention it could at best be more confusing and at worst cause serious accidents. Employers should ensure that their engineers are doing things right and setting standards that we can all understand.
I would love to hear your views; maybe you have misread a drawing?
Cheers
Bob