# Sealed Solenoids Suspended in a Hydraulic Chamber

#### squatchy

Joined Nov 21, 2012
43
Let's say I have multiple solenoids. They are sealed, so that when they are suspended in the hydraulic solution of a hydraulic chamber, they displace a certain amount of fluid with their plunger, and that amount of displacement varies depending on whether the solenoid is active or not.

Could I put multiple solenoids inside the chamber, as illustrated, and control the master plunger (of the hydraulic chamber) to varied degrees depending on which solenoids were active/inactive?

Thanks!

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#### spankey666

Joined Nov 30, 2011
91
only if the solonoids are outside the chamber, but the moving actuator sealed and protruding into the chamber will it work.
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#### squatchy

Joined Nov 21, 2012
43
only if the solonoids are outside the chamber, but the moving actuator sealed and protruding into the chamber will it work.
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What would be the conflict if the entire solenoid were basically sealed inside the chamber?

#### tshuck

Joined Oct 18, 2012
3,535
I'm sorry to keep putting a damper on your theories, but an increase in temperature will cause an increase in pressure... the piston moves out... at this point, any sort of accuracy you wanted out of this is shot.

Also, you would need to take into account the fluid mechanics, specifically, the compressibility of the fluid.

#### squatchy

Joined Nov 21, 2012
43
I'm sorry to keep putting a damper on your theories, but an increase in temperature will cause an increase in pressure... the piston moves out... at this point, any sort of accuracy you wanted out of this is shot.

Also, you would need to take into account the fluid mechanics, specifically, the compressibility of the fluid.
Don't be sorry... I appreciate it! All excellent points. This is how I learn.

#### WBahn

Joined Mar 31, 2012
25,076
The basic idea is fine, but there are a number of fine points to consider. If the volume of the unit containing the solenoid and plunger is changing, that means that there is some region within the solenoid that is experiences equal changes in volume and resulting changes in pressure.

As the temperature of the fluid changes, so too will it's volume. This will have the same impact as your plungers moving out. So you need to look at the coldest to hottest fluid temperatures you will see (and note that it is the fluid temperature that counts and hydraulid fluid that is being worked get pretty hot) and consider the volume expansions that are involved compared to those you are trying to achieve. If it turns out that it is an issue, one option is to use a temperature controlled solenoid to move a plunger so as to compensate for the thermal expansion of the fluid. You can even devise a purely mechanical means of doing this automatically.

#### BillB3857

Joined Feb 28, 2009
2,516
As the plunger moves out, (or in) hydraulic fluid would move in (or out) to fill (or vacate) the space within the coil previously occupied by the plunger. Net gain/loss of volume = zero.

#### Ron H

Joined Apr 14, 2005
7,014
As the plunger moves out, (or in) hydraulic fluid would move in (or out) to fill (or vacate) the space within the coil previously occupied by the plunger. Net gain/loss of volume = zero.
I agree. The only way I could see this working would require that the solenoid be enclosed in a relatively large, gas (air) filled chamber, so that the change in internal pressure, due to change in displacement, could be easily overcome by the solenoid.

#### WBahn

Joined Mar 31, 2012
25,076
As the plunger moves out, (or in) hydraulic fluid would move in (or out) to fill (or vacate) the space within the coil previously occupied by the plunger. Net gain/loss of volume = zero.
Not if it is sealed. Imagine a run of the mill single-acting actuator. Normally, the end without the oil is vented so that air can move in or out of this chamber as the piston moves in and out. But now put the piston in the fully retracted position and seal the vent. Now, when the piston moves out it compresses the air in the non-oil side instead of it venting. There are some pistons that are made this way because the compressed air will help to retract the actuator. In fact, many cylinders not only seal this chamber, but actually pressurize it for this very purpose.

So if you would take one of these cylinders and put it inside another cylinder (or just submerge it into a fluid), you would see the fluid displaced by the volume of the rod. If you now removed the fluid and fittings from the actuating side of this actuator and replaced it with a solenoid, you would have what he is talking about.

#### WBahn

Joined Mar 31, 2012
25,076
I agree. The only way I could see this working would require that the solenoid be enclosed in a relatively large, gas (air) filled chamber, so that the change in internal pressure, due to change in displacement, could be easily overcome by the solenoid.
The volume of the gas chamber wouldn't have to be that big. A much bigger concern would be the difference between that pressure and the pressure in the chamber the thing is setting in. That's what the solenoid is working against.

#### Ron H

Joined Apr 14, 2005
7,014
The volume of the gas chamber wouldn't have to be that big. A much bigger concern would be the difference between that pressure and the pressure in the chamber the thing is setting in. That's what the solenoid is working against.
Good point. I was assuming that the output plunger of the hydraulic chamber would be under low load, but that might not be the case.