Pressure Gauge Sticking

If your pressure excedes the full scale value of the pressure gages then damage could have occured. If the new pressure gages are not liquid filled, they may have vibrated to death.

Pressure would have to be turned up by the operators. we use around 150-200 psi in the process. the gauges are 0 - 600 psi and the line pressure is 0 - 5,000 psi.

yes they are oil filled.

Both are Wika gauges 1 is 2 1/2" the other 4"

"we use around 150-200 psi in the process. the gauges are 0 - 600 psi and the line pressure is 0 - 5,000 psi." I'm rather confused by this statement. You have 5000psi in your pressure line, but are only using 150-200 psi in you process. Are you using a pressure reducing valve? is the HPU (hydraulic power unit) a central unit running many different processes? What is the absolute maximum pressure that can be read from the point where your gauges are in the system? There are numerous ways of getting things done in hydraulics, finding the best solution to the problem takes a lot of questions and answers.

Woo-Woo!

I am hoping this employee candidate scored high enough to be hired as the newest member of the LynDoor™ Industries crew. Have you spoken to her about the upcoming Antarctic Submarine Expedition?

On subject, I also agree with RVZ717. Shop guys sometimes like to alter settings, in some misguided belief that more pressure is gooder/faster/better.

Used to build (I didn't really build anything, I was engineering _^manager) process equipment with dozens of pumps, spraybars and controls. Some were 100's of feet long.

It was nearly impossible to keep the operators from "helping" by tweaking the knobs. Gee, I'zz just fine tunin' it, they'd say. They had no idea what they were doing.

I've invited this particular candidate on a short submarine shake down cruise. She was skeptical until I assured her that we WERE NOT RACING THEM.

Sudden spikes and drops in pressure can cause guages to fail. This is common in construction and farm machinery especially on rough ground. Even though the operator may only see constant pressures spikes and drops can be lightning fast and tough to catch.

Another source of guage failure in the machinery I work with is foreign material getting into them. The tiniest flake of brass from the pump can jam things pretty effectively.

RVZ717,

Thanks, thats kind of what i figured happened. Other parts of the press use high pressure. The injection pressure is low and what we want to control. Transducer would be the way to go but depends on our customer ($$) we will check to see if there is a different point where we can measure from. Dummy knobs will not work, the operator needs to vary pressure depending on the model to mold. Parts are small 1/2" to 3" long and 1/4" dia. (miniture sliprings)

Thanks all for the help!

Would a 6,000 PSI Reducing Regulator work? If so, should it be set to max. gauge pressure to eliminate damage or just a general setting like 200 psi? (just above user range)

Thanks all

What's wrong with using two gauges? One 0-6,000 PSI set at 600 PSI, then the

0-600 PSI guage downstream of that for fine adjustment.

Sorry,

Obviously there are some valves in the line, too.

As said earlier your gages have been damaged by overpressure.

What we have done in these cases is to install a shut off valve in front of the lower pressure gage. Open the valve to set your lower pressure settings when it is determined by the 0-6000 gage to be safe, and then close the valve after setting the pressure to protect the lower value gage.

It is fairly unusual to see 150-160 psi injection pressure.

More commom to see that pressure as "backpressure".

If you are truely using 160 PSI injection pressure on a 5000 PSI machine it is similair to cracking a peanut with a sledgehammer... it works but not very well!

Hydraulic control below 200 PSI or so is not that easy to do with modern higher pressure systems. you are trying to control to less than 10% of the rating. Recalibrating the machine with replacement low pressure springs to a maximum of 1000 psi may help.

MIKE L.

Parts are very small, about the size of a 1/2" long straw. There are small rings with wires welded to them. (sliprings) On some models they flash or leak plastic out the lead exits.

If you are truly trying to control 5000 psi down to 150 psi then some control issues come up.

If the reducer is installed in the outlet port of the directional control valve. the reducer sees no pressure and will therefore be "open" waiting for pressure. When the directional valve finally shifts, the reducer will (not may) overshoot before it decides to regulate the flow sufficient to control the pressure.

From a control stand point the reducer is installed in the pressure port to the directional control valve. thus the reducer is constantly reducing the pressure and is "ready" to control the cylinder pressure. Down side is that the reducer is constantly "using" oil to control the pressure, this will add heat to the system and will wear the reducer quicker.

RVZ717 nailed it with his assessment that the gauges' bourdon tubes have zero tolerance for overpressure, and get stretched beyond their elasticity point at which point, they are process rezeroed and the condition can not be corrected. The gauge is trashed.

The recommendation for dual guages at high and low ranges with individual shutoff valves is probably the least expensive route, but there are gauge protectors designed to protect a gauge against overpressure.

Typically, an internal spring is loaded to "trip point". Pressures above the trip point trigger positive shutoff between the process and the gauge's process port thereby protecting the gauge internals from the pressure. The line pressure typically has to drop to about 10% less than the trip point before the spring/plug will reset and open the shutoff valve.

They look something like this: