Double Solenoid Valve , three position valve?

Tofo

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Join Date
May 2013
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I 'guess' I understand what is signal solenoid valve. Most of them are spring return with air pilot. It will move HOME position if electrical energy is off

Double solenoid valve use two solenoid. That make the cylinder (if the valve is connected to a cylinder) to stay the same position even if electrical energy is off.

Now what is three position valve?
I understand that could make 3 stages (Please tell me if I misunderstand that).
Does it has to be a double solenoid operated?
How about any specific feature of a three position valve?
How two or one solenoid make three position??

Thanks
 
Three position is a "center off" valve typically used to control a double acting cylinder. One solenoid ON to extend, the other ON to retract, stationary when both coils are off.
 
Three position is a "center off" valve typically used to control a double acting cylinder. One solenoid ON to extend, the other ON to retract, stationary when both coils are off.

Does this mean there is NO exact location of the cylinder will move during stationary state?
 
Does this mean there is NO exact location of the cylinder will move during stationary state?
Three position valves have a number of variants. Depending on the valve configuration, the center position could be:
1. Exhausted - Air is released from both sides; cylinder is free to move.
2. Pressurized - Air is applied to both sides of the cylinder simultaneously.
3. Closed - Ports on both sides of the cylinder are blocked, trapping the air inside. This is typically used to hold the cylinder in place during an Estop, in cases where a total air dump could be dangerous (i.e. vertical motion).
 
The way to think of 3 way solenoids is like a form C relay contacts. You have a common port, a normally open port (that is connected to common with no power) and a normally closed port (closed to common with no power). When the solenoid fires the common port connects to the NC ports.
 
The way to think of 3 way solenoids is like a form C relay contacts. You have a common port, a normally open port (that is connected to common with no power) and a normally closed port (closed to common with no power). When the solenoid fires the common port connects to the NC ports.

I don't think that's really the best comparison. I can't think of a better comparison, but comparing it to a relay does not really promote the proper understanding. In order for the valve in question to be anything like a relay, the relay would need be tri-state and have two coils, and a center off position, along with several contacts to arrange a polarity swapping configuration. Then, trying to explain how a relay like that would operate, would be the exact thing that we are trying to explain with the solenoid valve, but more confusing and with more hypotheticals.

The best way to understand this IMO is to look at the hydraulic schematic symbol and trace out the fluid flow in each position; visualize that little 3-box block shifting to the left and to the right, and figure out what will happen in each position. If you don't know how to read hydraulic schematics, google that. There is plenty of info out there.

EDIT: the closest electrical analogy I've been able to think of is a mechanically interlocked motor reversing contactor pair.
 
Last edited:
I don't think that's really the best comparison. I can't think of a better comparison, but comparing it to a relay does not really promote the proper understanding. In order for the valve in question to be anything like a relay, the relay would need be tri-state and have two coils, and a center off position, along with several contacts to arrange a polarity swapping configuration. Then, trying to explain how a relay like that would operate, would be the exact thing that we are trying to explain with the solenoid valve, but more confusing and with more hypotheticals.
I think Bullzi's analogy is valid for a 3-way valve, but the OP was asking about positions, not ways. His questions imply that he is using a 4- or 5-way valve.

The only problem I have with the relay analogy is potential confusion over the term "closed." With a relay it refers to contact closure (and resulting current flow), whereas Bullzi uses it to refer to a blocked port. Basically the logic is reversed.
 
Here is an example of a 3 way valve with 2 solenoids.

86290safeapplic_00000058907.jpg
 
The pictured valve is actually a 3-position, closed center, 5-way.

In the center position (both solenoids off), the cylinder ports are blocked, trapping the air in the cylinder.

The number of ways is generally determined by counting the number of ports. 4- and 5-way valves are normally used for air cylinder applications, where pressure and exhaust need to swap sides when the valve shifts. A 4-way has a common exhaust, whereas a 5-way has separate exhausts for each side. 3-ways are typically used as air dump valves.
 

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