2
\$\begingroup\$

This is my first question so please let me know what improvements can be made, if I need to edit things, etc.

I've recently salvaged a heating element from an old single cup coffee machine that I want to use for an automated brewing machine. I want to include a holding tank, much like commercial units, that would hold about a litre or two of water and be mounted above the heating element. The water is going to be gravity fed into the heating element and I'm considering using a solenoid valve below the tank to shut off the flow of water so that I can control the amount of water boiled at one time. I'm not terribly mechanically inclined, so my question is how do I determine the "size" of solenoid valve needed?

I checked around for similar questions on this site, but most I found were about how to drive the solenoids or "can I use X to power solenoid Y" type questions. If there is an already answered question, if someone could point me to it, then I will gladly close this one.

Thank you for your time.

Edit: Link to solenoid valve removed, as it was determined that the valve will not work in this given situation (as mentioned by DrFriedParts).

\$\endgroup\$
  • \$\begingroup\$ I agree with DrFriedParts answer, but I am just going to accept the answer I provided, as I feel it provides a bit more information for people who may have a similar issue choosing the correct valve. If others have a better answer, I will gladly take that over the one I provided. \$\endgroup\$ – Luc Jul 5 '13 at 12:41
3
\$\begingroup\$

Bad datasheet?

You should be aware that the datasheet linked is most likely not the correct one for the valve you will receive if you buy through that link. Various user comments and even the official description suggest this.

Wrong architecture?

This is not the right type of valve for your application:

Note: This is not a gravity-feed solenoid. This means that you will need enough water pressure to fully open the valve. Check the datasheet below for exact details. It operates at a minimum of around 3 PSI

Your application (coffee maker) is most-likely gravity-fed. That means you have a tank of water and you let it out into your machinery for use driven solely by its own weight. With this valve, you will not be able to fully drain the tank. As the level gets lower, the pressure on the valve will decrease to the point that the valve won't open.

If you are using this valve you will need a pump on the tank-side of the system.

Wrong forum?

The detail of mechanical actuation and pressure systems is probably better handled on one of the mechanical engineering or physical sciences forums.

\$\endgroup\$
  • \$\begingroup\$ Yes you are absolutely correct, I added the link to that solenoid valve as an example, but thank you for pointing out the issues with it. I'll try asking around on another forum, but thank you for your insight. Which forum do you think I would receive the best information from? \$\endgroup\$ – Luc Jul 2 '13 at 19:53
2
\$\begingroup\$

Upon further research, I have determined that for this specific application, a solenoid valve designed specifically for a gravity fed systems is needed. I found that the valve here should work for the given application. The pressure rating for this type of valve gives the maximum container height allowed where the valve can still open and close properly (in this case 7 ft). Although there are a number of different factors which would affect the choice of valve:

Valve Type:

There are numerous different types of valves, but the valve found at the above link is a direct-drive type valve where the solenoid directly moves the valve plunger. Other valve types operate differently, for example pilot operated valves utilize the line pressure for operation instead of relying solely on the solenoid. Another important point is whether the valve is to be normally opened, or normally closed (what state the valve is in when it is not energized). My understanding is that choice of valve type depends on the fluid in the system and the pressures involved.

Pressure Rating:

The pressure rating, in this case (gravity-fed system), gives the height of fluid that the valve can retain before it fails to operate properly. However, some valves also require a minimum pressure to open. In the case of the gravity-fed system, the pressure is dependent only on the height of the fluid in the container before the valve, not on the width or other dimensions of the container (Hydrostatic Paradox).

Fluid Type:

Different fluid types generally require different valve materials. For example, based on this document (page 526), sodium hydroxide requires a stainless steel valve assembly. It is also necessary to consider the temperature of the fluid in question, as that will also affect which valve material is needed.

Actuation Speed:

Actuation speed depends on valve size and type, with smaller valves operating faster than larger ones. Solenoid valves that utilize a DC supply will also actuate 50% slower than equivalent AC valves (as mentioned here on page 512).

Supply Voltage:

Solenoid valves are available in a number of different supply voltages, which provides options for different systems, i.e. a given system may not have 24 V available, so a 12 V valve would need to be used, etc. Also, as mentioned above, AC valves operate faster than DC ones.

It may also be worth considering the number of actuations requried per second and the duty cycle requried for a specific coil (some will overheat if energized continuously). Please correct me if I'm wrong on any of the information I have provided, but that is what I found regarding the subject.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.