MOOG Servo Valve

Hi guys,
We are planning to operate a piston using a MOOG servo valve 77-507.
Idea is to move the piston with certain variable forces and achieve some tasks.
Currently we just have this valve.
I will be thankful if one could explain what hardware is required (amplifier) and basic working principle so that I could explain to my electric controls guy for automation using delta PLCs.

Thanks in advance.
 
Judah,

This is question best asked of a MOOG authorized re-seller. You need to ascertain what kind of electrical configuration the servo-valve you possess has, and then they can tell you what is required.

1621976018912.png

The table above is from a data brochure for 77 Series servo-valves from the MOOG website ( Servovalves.PDF (moog.com ). I have a feeling there is more numbers/information from the nameplate or package they will require in order for them to tell you how it works. There are coils which use 4-20 mA, 0-10 mA, 0-200 mA, and +/- 10 mA, and probably other current signals as well. There are single coil servos, two-coil servos, and three-coil servos.

Please work with an authorized MOOG distributor or MOOG itself to ascertain what will be required, based on what you have--or may actually need depending on how it will be used. They will ask things like how much hydraulic flow is estimated to be required; what is the hydraulic medium (mineral-based oil or synthetic oil or ???), how big is the volume of the cylinder, how fast does the piston/rod need to move, and is the piston double-acting or single-acting--and that's probably just for starters. But, in my experience a good distributor application engineer or an application engineer from MOOG itself can help identify what is required for the application and then can tell you if what you possess will work, and what will be required to drive the servo as necessary to achieve your needs.

Best of luck!
 
Thanks a lot CSA.
I have answers to all your mentioned questions.
At the moment, I am waiting for someone from MOOG to contact me. Hopefully they would.

I spoke with my control guy. He tried to input -10V to 10V (through analog output) instead of current and managed to move the piston (its a double acting cylinder). I am not sure if he ruined the valve!
We tried to zeroing the valve mechanically and did get success but the moment power was turned on, even with zero volt input, piston moved. Upon then, he wrote some offsetting functions to stabilize the piston (software zeroing). This way, by inputting -10V to +10V piston did move in both ways.
I think by doing so, motor did draw the needed current but the movement was probably not according to the graphs provided on the datasheet.



Judah,

This is question best asked of a MOOG authorized re-seller. You need to ascertain what kind of electrical configuration the servo-valve you possess has, and then they can tell you what is required.

View attachment 1295

The table above is from a data brochure for 77 Series servo-valves from the MOOG website ( Servovalves.PDF (moog.com ). I have a feeling there is more numbers/information from the nameplate or package they will require in order for them to tell you how it works. There are coils which use 4-20 mA, 0-10 mA, 0-200 mA, and +/- 10 mA, and probably other current signals as well. There are single coil servos, two-coil servos, and three-coil servos.

Please work with an authorized MOOG distributor or MOOG itself to ascertain what will be required, based on what you have--or may actually need depending on how it will be used. They will ask things like how much hydraulic flow is estimated to be required; what is the hydraulic medium (mineral-based oil or synthetic oil or ???), how big is the volume of the cylinder, how fast does the piston/rod need to move, and is the piston double-acting or single-acting--and that's probably just for starters. But, in my experience a good distributor application engineer or an application engineer from MOOG itself can help identify what is required for the application and then can tell you if what you possess will work, and what will be required to drive the servo as necessary to achieve your needs.

Best of luck!
 
Judah,

The documentation, even from MOOG, for some of these servo-valves isn't very good. The MOOG servo-valves I have most of my experience with are bipolar--meaning they accept positive and negative current (-10 mA to +10 mA). The coils have a resistance of 1000 ohms, and there are either two coils or three coils. The idea is that when the current being applied to the coils is 0 mA* (I'll explain the asterisk below) the flow of hydraulic fluid into and out of the servo valve will be zero--so that for all intents and purposes no hydraulic flow will flow into or out of the servo to or from the hydraulic piston (actuator). The polarity of the current decides which direction the flow of hydraulic fluid through the servo valve will be flowing, and the magnitude of the current decides how fast the flow of hydraulic fluid will be. Sometimes these valves are referred to as velocity devices, because the magnitude of current being applied determines how much hydraulic fluid flows to which side of a double-acting piston, thereby controlling the speed at which the piston moves.

SOME of the servo-valves have a special spring which, in the absence of any current at all (such as when the control system output fails or there's a break in the circuit) the flow of hydraulic fluid through the servo-valve will cause the actuator to move to a fail-safe position (such as to shut off the flow of fuel or air or steam to protect a piece of equipment from damage when there is no signal from the control system). In order to get the actuator to remain in a steady-state position (that is not to move in one direction or the other) a small amount of current needs to be applied to the servo valve coils with the appropriate polarity so as to overcome the spring tension and stop the flow of hydraulic fluid to or from the hydraulic actuator. This spring is sometimes called the fail-safe spring, and the amount of current required to overcome the fail-safe spring's tension and interrupt the flow of hydraulic fluid to or from the hydraulic actuator is sometimes called the null bias current (null because it holds the hydraulic actuator in a "null" position--not moving, and remaining in a desired position, and bias because it's a small amount of current added to the output which makes the output non-zero.

But, MOOG or a MOOG representative will be able to be of more help and explain how the valve in your possession works. And, what's required to make it work in the way your application requires.

Best of luck!
 
Thanks for the explanation! Really appreciate that.
Sure, MOOG should help.

Have a great day ahead.

Judah,

The documentation, even from MOOG, for some of these servo-valves isn't very good. The MOOG servo-valves I have most of my experience with are bipolar--meaning they accept positive and negative current (-10 mA to +10 mA). The coils have a resistance of 1000 ohms, and there are either two coils or three coils. The idea is that when the current being applied to the coils is 0 mA* (I'll explain the asterisk below) the flow of hydraulic fluid into and out of the servo valve will be zero--so that for all intents and purposes no hydraulic flow will flow into or out of the servo to or from the hydraulic piston (actuator). The polarity of the current decides which direction the flow of hydraulic fluid through the servo valve will be flowing, and the magnitude of the current decides how fast the flow of hydraulic fluid will be. Sometimes these valves are referred to as velocity devices, because the magnitude of current being applied determines how much hydraulic fluid flows to which side of a double-acting piston, thereby controlling the speed at which the piston moves.

SOME of the servo-valves have a special spring which, in the absence of any current at all (such as when the control system output fails or there's a break in the circuit) the flow of hydraulic fluid through the servo-valve will cause the actuator to move to a fail-safe position (such as to shut off the flow of fuel or air or steam to protect a piece of equipment from damage when there is no signal from the control system). In order to get the actuator to remain in a steady-state position (that is not to move in one direction or the other) a small amount of current needs to be applied to the servo valve coils with the appropriate polarity so as to overcome the spring tension and stop the flow of hydraulic fluid to or from the hydraulic actuator. This spring is sometimes called the fail-safe spring, and the amount of current required to overcome the fail-safe spring's tension and interrupt the flow of hydraulic fluid to or from the hydraulic actuator is sometimes called the null bias current (null because it holds the hydraulic actuator in a "null" position--not moving, and remaining in a desired position, and bias because it's a small amount of current added to the output which makes the output non-zero.

But, MOOG or a MOOG representative will be able to be of more help and explain how the valve in your possession works. And, what's required to make it work in the way your application requires.

Best of luck!
 
The valve is a pretty good valve for most purposes. Fortunately CSA posted a link to the pdf. (good going CSA). Judah, you should always post a link to the valves you are using yourself because sometimes the valve data is hard to find. Judah, use an ohm meter to measure the resistance of the coils. This will provide a hint as to how to wire up the coils. The coils can be in series or parallel depending on the current supply. Applying +/- 10 volts should not hurt the valve but it could hurt the power supply depending on the impedance of the valve. Measure the impedance of the coils.

Most PLCs have analog cards that will output +/- 10 volts but what servo valves need is current. Most systems will require a +/- 10 volt to +/- current converter like this:
https://deltamotion.com/pdf/vc2124.pdf

Judah, you really should state what you are trying to do in detail. A PLC may not be able to control a hydraulic servo system well.
If you are the hydraulic designer, you should read this first.
Also, there are a lot of good articles on Hydraulics and Pneumatics magazine.
 
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