Choosing the Best Valve: Ball vs Solenoid for Reliable Flow Control

[Aki]

Hi,

I want to know the difference between an actuated ball valve and a solenoid valve. Which one is more reliable? I want to program the valve so that it allows flow for 10 seconds to one outlet and after that direct the flow to the second outlet. I know I'll probably need a 3-way valve. But which one is better, ball or solenoid?

Thanks!

 

[Integral]

A solenoid is a electo-mechanical device which activates a valve. We have solenoid activated ball valves. So you may want to to a bit more research.

Generally a ball valve is a on/off device, it does not direct flow to different ports. For this you need a 3 way pneumatic valve.

Look around http://www.smcusa.com/sections/products/valves.asp" and
http://www.parker.com/ead/cm2.asp?cmid=10041" for more info.

 

[Aero Stud]

No, he's actually right. I searched the subject cause I don't about these things either and wanted to find out a bit. And I think you're right Aki that you need a 3 way ball valve if you want what you described.
http://en.wikipedia.org/wiki/Solenoid_valve
http://en.wikipedia.org/wiki/Ball_valve
http://en.wikipedia.org/wiki/Globe_valve
http://en.wikipedia.org/wiki/Gate_valve

 

[FredGarvin]

The OP needs to be more precise. A solenoid actuates a valve. A ball valve is a type of valve. Most solenoid valves are usually a type of plug or globe valve. Especially 3-way valves. The generic terminology for an actuated hydraulic valve is a solenoid valve, but that utilizes a sliding spool to direct flow to the proper port.

If the OP is referring to a hydraulic 3-way valve then there are of course differences and the questions being asked are too vague to answer properly.

Which one is more reliable?

It depends on the application. In terms of simplicity, the actuated ball valve wins out. It can handle a lot more different types of fluids and is much more tolerant of fluid contamination. A ball valve will also, most likely, have better flow capacity for a given size. On the other hand, the hydraulic valve, depending on the features, can be positioned/ported to provide more flow options and can tolerate higher pressures.

which one is better, ball or solenoid?

Again, we can't answer. Each has its own designed purpose. If you post the fluid operating parameters and exactly what it is you are trying to accomplish along with other things like the budget you have to work with, we can help you.

 

[Q_Goest]

Hi Aki,
Either valve can work in principal. Both ball and solenoid valves can be automated and can come in a variety of port configurations. In general, solenoids are low power (ie: about 100 watts, max) so they are used primarily on relatively small valves where line size is an inch or less, and at low pressure, up to a few hundred psi. There are exceptions to this. Some solenoid valves in the aerospace and hydraulic industries can operate at many thousands of psi, but they are generally for very small line sizes, about 1/2" or less.

There are also different types of configurations for solenoid valves:
- Direct acting (the solenoid acts directly on the valve plunger/spool)
- Indirect (such as shown in the wiki article that Aero posted)

The indirect acting are generally larger in size and can handle higher pressures, but they require a minimum pressure drop across the valve to open. That's generally not a problem, but can be at times.

Ball valves are generally for higher flow rates, and the actuators needed to move them are generally much larger too. They can be made with a variety of port configurations, just like solenoid valves.

I'd suggest posting what you know about the valve's requirements including:
- Fluid type
- Line size (pipe or tube diameter)
- Temperature range of the fluid
- Ambient temperature range
- Maximum pressure the valve is needed for
- Process flow rate
- Acceptable pressure drop across valve
- How fast it must actuate in seconds or milliseconds
- If "instrument air" is available (sometimes called "shop air": 50 to 100 psi air).
- Price range

Note that solenoid valves and ball valves are generally for on/off service. If you're looking for flow or pressure control such as from a control loop, these won't generally work.

 

[Aki]

Thanks for your replies

I'm building a LOX-Kerosene fueled rocket. I need some fuel that goes to the igniter for the first 10 seconds, and then the rest of the fuel goes to the main combustion chamber for 90seconds.

The flow rates and other properties are:
LOX: 1.5 L/s , -186 degree C , Cv=3.82
Kerosene: 0.94L/s , 15 degree C, Cv=2.01

both can drop from 175psi to 130 psi , 3/8" tube diameter (although I wouldn't mind if it was bigger/smaller)

We plan to spend at most $400 for each valve, and it would be best if it can actuate in milliseconds

I'm looking into the ball valves from Worcester and they are huge...

 

[Ronnin]

Thanks for your replies

I'm building a LOX-Kerosene fueled rocket. I need some fuel that goes to the igniter for the first 10 seconds, and then the rest of the fuel goes to the main combustion chamber for 90seconds.

The flow rates and other properties are:
LOX: 1.5 L/s , -186 degree C , Cv=3.82
Kerosene: 0.94L/s , 15 degree C, Cv=2.01

both can drop from 175psi to 130 psi , 3/8" tube diameter (although I wouldn't mind if it was bigger/smaller)

We plan to spend at most $400 for each valve, and it would be best if it can actuate in milliseconds

I'm looking into the ball valves from Worcester and they are huge...

http://www.parker.com/ead/cm1.asp?cmid=311

You may want to have a look there and see if any of the industrial valves Parker offers could fit your need.

 

[FredGarvin]

Getting a Cv of 3.8 and 2.01 for a 3/8" tube size may be a chore. That's pretty big. I routinely use a very special made 28VDC solenoid for 1/2 ports that has a Cv of 2.5 and it is considered large (very large for a direct acting solenoid). The cryogenic aspect isn't going to help matters.

When you say actuation in milliseconds, I hope that's on the range of 50-100 or so.

Do you have a weight target for each valve?

I would recommend looking at Valcor for their valve lines to see if they have anything that may work.

 

[Q_Goest]

Fred, you beat me to it again… <sigh> ;)

I'd agree that the Cv you're looking for in a 3/8" tube isn't realistic. Try at least 1/2".

Are these valves intended to go on the rocket itself, or on the ground portion?

Regarding a LOX valve:
Worcester ball valves are fairly expensive, and you should use an extended stem. They have electric motor operators as an option, but they're very slow (seconds, not msec). And cost is well above $400.

You could also use a globe valve with extended stem and air or motor actuator, but they'll get expensive too. $400 isn't enough unless you don't want the actuator.

I'd suggest a solenoid valve for this. Try Magnatrol, Parker (Skinner), and ASCO. They should have something in your price range with the features you need. They can be used for the Kerosene too. As Fred mentioned, Valcor certainly can do it as well, and they'd be a good one for a flight valve too, but (correct me if I'm wrong, Fred) they're a bit expensive. If you look into Valcor, I'd also suggest Marotta Scientific Controls, Circle Seal, maybe a few others. They specialize in flight hardware, but they'll be quite a bit more expensive. On the flip side, they can also test your valve to specific g loads and vibration levels, so reliability gets better.

Also, as Fred mentioned, these aerospace valve mfg's often use 28 VDC, but I would think they can also do 24 VDC or maybe 120 VAC.

Just a quick note about materials of construction: the LOX valve should be brass with Teflon or filled Teflon trim. Kel-F, now called Neoflon, is also good. Elastomers won't handle the cold, except for warm parts (on extended stem). Piping should be copper, which you can insulate (vapor barrier especially important). Cleaning is extremely important.

 

[FredGarvin]

You're right about Valcor not being cheap Q. They are pricey. However, to get the performance that is being asked for, the OP is going to have to pay up. $400 is possibly going to cover the valve but not a valve with an actuator. It's about 1/10th of the cost for a performance valve worthy of being used in a rocket application.

A while back I was working on a new kind of rocket engine and I was in touch with a company that was very small. They built the main valve used to control the Tomahawk rocket engine. I talked to they're head engineer and researcher. I wish to heck I could remember the company's name. I will look for it tomorrow. They weren't able to accommodate my request for a small purchase amount of valves, but perhaps things may have changed. I will work on getting you that company's name tomorrow.

Q mentioned Asco. They make all kinds of solenoid valves. They may meet some of your requirements. I would say that, on the inexpensive side, they may be your best bet. They're easy to get, inexpensive and come in a lot of materials and configurations. Again, you won't get the Cv you want.

 

[Aki]

Just a quick note about materials of construction: the LOX valve should be brass with Teflon or filled Teflon trim. Kel-F, now called Neoflon, is also good. Elastomers won't handle the cold, except for warm parts (on extended stem). Piping should be copper, which you can insulate (vapor barrier especially important). Cleaning is extremely important.

Would stainless steel be compatible with LOX, and what using brass for kerosene?

Is true that ball valves in general are bigger than solenoid valves because ball valves need an extra actuator?

I've looked at the Valcor cryogenic valves, and they either have a Cv that is too small or the pressure isn't large enough... I'm going crazy trying to find the correct valve. I'm going to take a look at the other companies that you've suggested.

Thanks for your help guys!

 

[Aki]

What would happen if I use a valve that has a Cv lower/larger than the one that I calculated?

 

[Q_Goest]

Stainless steel is generally considered acceptable for LOX, though it can ignite at higher pressure and temperature. Generally we use brass or copper alloys simply because they can't ignite in oxygen.

Do you know how to calculate flow as a function of pressure? A lower Cv will increase pressure drop across the valve.

 

[Aki]

Do you know how to calculate flow as a function of pressure? A lower Cv will increase pressure drop across the valve.

Yes I know how to find the Cv for a fluid: Q=Cv*root(change in pressure / specific gravity)

But I do not know how to find the Cv of a gas

 

[Q_Goest]

Hi Aki,
I had a look around for a decent reference on calculating flow rates through valves. There’s a bunch of good information here:
http://www.engineeringtoolbox.com/control-valves-t_45.html

With the equations for gas and other phases here:
http://www.engineeringtoolbox.com/flow-coefficients-d_277.html

Note that flow coefficient (Cv) is a single value given to a valve which is intended to quantitatively characterize how pressure, temperature, density and flow relate to a specific valve. That value, and the equations used are reasonably accurate, but they are not exact. The flow coefficient can be derived by testing the valve on air or water, or any fluid for that matter. The equations that quantify the valve’s flow capacity are than applied depending on the phase of the fluid. The point here is that testing of the valve can be done using a host of different fluids, but the actual flow using different fluids may be off to some degree. I’ve seen these things off by 10% or even more.

I wonder why your values for Cv are so exact (three significant digits). Are you thinking that you will control the flow rate using this valve? How are you getting the correct stoichiometric mix of O2 and Kerosene to the engine? And for that matter, how are you pressurizing the fluids?

Note that flow rate of the LOX will depend strongly on liquid conditions in the tank because as pressure drops, flashing will occur, especially across valves where restriction is highest. The equations above only cover single phase flow (and steam).

 

[Gokul43201]

Have you (Aki) looked into ASCO? They make solenoid actuated cryogenic valves - specifically used for cryogenic fluids. I've used one of their cryovalves to build a PID controlled delivery system for Liq. N2 - I'm pretty sure it has a brass body. Typical prices are below $300 unless you really need a big Cv.

See, for example:http://www.coleparmer.com/catalog/product_index.asp?cls=24574

PS: Those are all 2-way valves. I'm not sure if they make a 3-way cryovalve, but you could call them and find out.

http://www.ascovalve.com/Applications/Products/Solenoid2WayData.aspx#Cryogenic
http://www.ascovalve.com/Applications/DistributorLocator/DistributorLocatorHome.aspx