How to Signal Pressure in a Hydraulic Line

Google pressure transducer

That's right. Specifically, Piezo transducer pads typically have a linear response-curve, in case you need a reliable, continuous reading over a range of pressure levels.

How about this:

Tap into the system and pipe to a solenoid valve that is parallel with a check valve that will dump back to the system. Beyond the solenoid valve have a pressure switch that will make when the unsafe pressure is reached(100 psi), it will turn on the warning light and close the solenoid and keep the pressure from building to level that will damage the pressure sensor switch--When the pressure in the system falls below 100 psi the check valve will open and the switch will open and bleed the pressure off, then, turn the warning light off.

The size and design of the valves can be worked out to handle the 30K pressure and you will be able to use any pressure rated switch.

Possibly?--Hope this helps.

Wow...that may be what I've been looking for. I'm going to have that option thoroughally investigated today. Kilgore Trout. You're not referencing Kilgore, Tx are you. Just curious...that's where I'm from. Anyway, thank you...

Kurt Vonnegut Jr. character, especially in Breakfast of Champions.

Good answers have been given.

The option with the solenoid is the best if no low pressure returnline is availabel.

I would prefer to use a 3 way pressure reducingvalve instead of a solenoid valve because of the risk during a during power drop or failure from the solenoid. In both cases the pressure switch would be destroied and probaly cause leakage.

Iff pressure builds up fast assemble a small restriction before the solenoidvalve. Please check with a mechanical meter iff the reactiontime from the valve is fast enough to prevent pressure increase above the allowed level from the switch.

For this reason a 2 way pressure reducing valve would also not work!

Good point, Guest!

Wire the pressure switch so that if safe pressure is present--open the solenoid and if undesired pressure is reached or power fails close the valve.

Wire the solenoid to the pressure switch N.C. contact with a system "on" indicator lamp and the warning beacon to N.O.

The system would have to be built with the possible failures in mind--redundant valves and and a means to isolate it from the system pressure manually for maintenance.

One thing to consider is that he needs something SIMPLE--No PLC and whether it is because of location or cost, designing a sophisticated sensor that isn't "off the shelf" may not be what he asked for.

Now we are getting somewhere--Good answer--You should login.

Looking into Safety related devices in pressure systems opens up a whole can of worms. What Safety Category/Safety Integrity Level are you working to?

You mention the pressure switch. It is for the application the best choice. You should use one which can be set a given pressure up to the hydraulic system maximal pressure. You should consider that all pressure switches have a hysteresis loop which leads to the fact that if the warning is on at as you suggest 100 it will go off at a lower pressure. It is possible to make a hysteresis free switch but it is not usual since they are used for regulation and without hysteresis loop there is a risk for oscillations around the set value.

Just wanted to say that I appreciate the responses that I've gotten here. I'm a Project Manager without engineering experience and your comments been very, very helpful. I did not respond to some comments. Please understand that I'm extremely busy and if your comment relates to something that I've already checked out, or is just a general question, I didn't take the time to respond. I sincerely appreciate your taking the time to contribute. Thank you...

A pressure transducer can be used from which signal is given to PID controller and through PID to Alarm Unit.

OR

A Pressure Switch(PS) can be set upto a certain limit (say 100psi) then from NO of the PS the signal (230v AC phase) is given to the coil of 230V Relay, then from NO of the Relay signal (230v AC phase) to the Siren or Alarm unit.

At that kind of pressure, I think you could make a device to attach to the exterior and detect the pressure. Either use a mount which would allow a contact to make as the line expands or change resistance as it expands.

A way to determine if this is possible is to get a dial indicator which has a V-block for the line to rest in and the indicator to be on the opposite side. Applying pressure should make it swell some and be detectable. If the amount is to small to activate a switch, two levers attached at a pivot point say 1 inch from two opposing V grooves could be made long enough to get usable travel to activate a switch or move a linear potentiometer for a reading.The further the indicator is from the V-grooves, the more travel will be available.

Think of it this way if you have trouble visualising my suggestion: put a finger from one hand between two fingers of the other hand. Start at the end of the fingers and move the one finger in toward your knuckles. As it move inward the fingers spread. the pivot point is your knuckles, the line your single finger, and the tips of the two fingers is where the indicator or sensor would go. Sliding the finger changes the ratio of pivot to line to sensor/indicator.

Most gauges use a somewhat flattened tube which tries to straighten out under pressure. They usually have a gear setup to move a dial for a reading.

At that pressure, I am sure you can find some way to use a non penetrating method.

If I am not clear enough, email me.

Good Luck!!!

There are lots of nuematic control options I would look at stainless tubing with high pressure switches or gauges to indicate that energy is applied

If you don't need much precision and want to save money try this.

Make a bend in a flexible section of the line and place a micro-switch there. When pressurized, the line will tend to straighten up and trigger the switch. You can adjust the trigger pressure by moving the switch position.

How about a stress-strain gage setup?

I work on Pressurewashers, what you could do is fit an unloader valve on the circuit, when pressure is in the circuit it is lifted off it`s seat then there is a visual difference, and if you require a limit switch on the end, it should be no problem, a take it the site is zone2 due to no electrical switches in circuit?

This is one idea and I believe, with the proper valves, will work:

1. Tap into the system pressure with a small line.

2. Install a manual shut off valve that can be operated if the safety light system fails.

3. Install a NORMALLY CLOSED solenoid valve wired to NORMALLY CLOSED contacts in the pressure switch, after the shut off.

4. Install a check valve parallel to the solenoid(Check against the system pressure).

5. Install a pressure switch, set to 100psi after both the solenoid and the check valve.

6. Wire the pressure switch NORMALLY OPEN to the solenoid and warning light.

7. Wire a pilot light to NORMALLY CLOSED contacts in the pressure switch.

Done.

You will have to ensure that the solenoid and shut off valve will handle the maximum pressure.

The idea is: The system pressure will build up to 100psi passing through the solenoid that is energized open and the pilot light will be lit. If the power fails the solenoid valve will close and the pilot light will be out.

Once 100psi is reached the pressure switch will change state and the normally open contacts will close and the normally closed contacts will open--When this happens, the solenoid will close and no more pressure will pass. At the same time the warning light will come on and the pilot light will go out. The check valve will hold the pressure back until the system pressure falls below 100psi--then will allow the 100 psi of pressure back into the system.--Ready for the next cycle.

Just wanted to say thanks. I sincerely appreciate it. What you have enabled me to do is to go to the engineers here and show them a better way to proceed than our company has been doing as regards safety warning lights. I was facing an uphill battle since I'm not an engineer and it is hard to make a bunch of engineers listen to a lowly Project Manager when I started telling them that there had to be a better way. This system or a variation thereof will probably be used world wide by FMC Technologies. I have had email communications from staff this morning when I got to work and they're liking your proposal as well. Thank you again.

I am happy to hear it!

I hope it gets the job done and prevents accidents, I had fun working this out.

K T