I need help on Hydraulic Solenoid Coils

Is there a correlation between voltage type (AC, DC)or reading (12 Volts, 220 Volts)and how much a coil heats up when it is powered for long time cycles. Or why do some coils run cool while others are hot enough to fry and burn meat?

I have a Solenoid operated Relief Valve that must stay energized throughout a cycle of up to 90 minutes. It is controlling Water Glycol Fluid (50% Ethylen Glycol/50% Water)that has a tendency to thicken up when held at elevated temperatures for long periods. Loss of water is the primary problem.

Does voltage type, AC/DC, have anything to do with assuring a cool/cooler coil while operating at current/voltage for extended periods.

You can tell from my question how extensive my electrical background is so take all the above into considerstion as you ponder the question. Detailed answers are welcome but may sail right by me.

Just like in hydraulic, in electricity it is important know the current ( flow ) as well as the volatage ( pressure ) drop to calculate the energy dissapated across at solenoid ( valve ).

You should be able to read the current required off the name plate of the relief valve or at least find the current required from the specications.

Are you sure it is the electrical power that is causing the valve to heat and not the oil flowing through the relief valve? I know a servo valve would take only about 20ma at 4 volts to open completely. That isn't much. I don't know why you need 120 volts. I would think the solenoid would be just pushing a little again or with a a spring that keeps the relief valve from opening or closing.

Do you have a link to the valve you are using?

Peter;

As you know I use valves in some unusual ways and I try never to use a Relief Valve to bypass excess fluid to tank. This relief valve is actually a Solenois Operated Shut-off Valve that keeps fluid in two single acting cylinders while tilting a large holding furnace. In essence the relief valve is being used as a large 2-wau shut-off like I show on page REL 8-9 in my Fluid Power Circuits Explained book. The other function is to relieve the pump to tank if there is some mal-function that would try to raise pressure above a safe setting.

At the end of a cycle the valve is de-energized and the furnace lowers controlled flow thru a flow control. It is also a way to lower the furnace in case of a power failure.

Here is a link to a page on the Vickers web site. The customer specified 24 VDC coils on everything on the circuit.


Page 30 shows coil info.

Page 31 shows the symbol on the middle left

Page 35 shows the valve dimensions

Most air solenoids switch only the control air which this air switches the spool so the electrity does a small portion of the work. In hydrualics it`s ussually different. They make control valves to where the electiricity switches the air this inturn switches the valve that is doing the work and there is no electrical used on the valve doing the work. We use these where it is to hot for the electrical coils to live.

I presume that since you are using a glycol soluiton you are operating a very high pressures unless its for environmental reasons. If you are at very high pressures then you probably do not have a pressure compensated pump, but a fixed displacement pump, hence the need for a relief valve instead of better ways to control pressure.

Using a relief valve is a very inefficient way to control pressure; it’s just the easiest way. The problem is that relief valves ALWAYS create heat. In any pressure application once the system reaches a static point, i.e., you are holding at a specified pressure, all the power generated at the hydraulic pump must be converted to heat somewhere. And when you have a relief valve, all that heat is generated right at the relief valve. So if you have a 35 KW pump motor and the pump never unloads, then you have to reject 35 KW of heat – and most of it ends up at the relief valve. That means that hydraulic fluid flowing over the relief valve is going to heat up fast, no matter what kind of fluid it is, and it can get very very hot. The first thing I would suggest is determining if the heat is coming from the fluid being dumped from a high pressure zone to a low pressure zone, or if it really is coming from the electrical solenoid. Your solenoid is likely to require about 35 watts, thats not a lot of heat.

We have several machines here that operate at 42,000 psi on a propreitary water based hydraulic fluid. We use an oil over water intensifier system to control pressure so that we can control the pressure using a directional control servo vave. But even in this system, when we begin to decompress, it develops temendous heat. We decompress through an array of orfices, and if you touch the valves or orfice blocks during the decompression sequence, even if briefly, you will get severly burned, it gets as hot as a stove and the fluid flashes to boiling water/steam as it crosses the orfices.




(This heating principle BTW can be used for finding internal leaks. If you have a cylinder or manifold that has a hot spot that is much hotter than it should be, you probably have a leak)

Alaric;

You evidently didn't read my post to Peter or the article on my web site titled "Designing Cool Hydraulic Systems."

The circuit is operated by fixed volume pumps with a total of 68 GPM. Each pump is ported to tank by a Normally Open Solenoid Operated Relief Valve and only sends fluid to the cylinders when they need to extend. Check valves at each pump outlet after the relief valve stop back flow and the Normally Open Solenoid Operated Relief Valve in my first post is energized to keep fluid from goung to tank.

Energizing the tank blocking relief valve and one to four relief valves at the pumps causes the furnace to tilt and dispense metal at any of four different speeds. De-energizing all solenoids lets the furnace down at a speed controlled by a flow control.

The maximum pressure is 1,200 PSI and and the water glycol is due to the fire hazard that mineral oil would be around a molten metal furnace.

There is no heat exchanger in the circuit since there will be no excess heat generated.

Bud, I just saw you other post and looked at your web site, looks like I probably didn't say anything you didn't already know.

Are these being used in a counter-balance type circuit?

Alaric;

Actaually there primary purpose is a soft shift 2-way normally open solenoid operated valve. They also serve as over pressure protection to the fixed volume pumps. See my circuit explanation in my last post.

fluidpower1 said:

Is there a correlation between voltage type (AC, DC)or reading (12 Volts, 220 Volts)and how much a coil heats up when it is powered for long time cycles. Or why do some coils run cool while others are hot enough to fry and burn meat?

I have a Solenoid operated Relief Valve that must stay energized throughout a cycle of up to 90 minutes. It is controlling Water Glycol Fluid (50% Ethylen Glycol/50% Water)that has a tendency to thicken up when held at elevated temperatures for long periods. Loss of water is the primary problem.

Does voltage type, AC/DC, have anything to do with assuring a cool/cooler coil while operating at current/voltage for extended periods.

You can tell from my question how extensive my electrical background is so take all the above into considerstion as you ponder the question. Detailed answers are welcome but may sail right by me.

Click to expand...

Coil voltages are usually based on the voltages available in the control cabinet or customer requests or parts availability or what the engineer likes.

Some coils are rated intermittant duty and some are rated continuous duty.

If you have an intermittant duty coil on continuously, it will get hot. If you have a condition that requires continuous operation of the coil, you need one for that condition.

Leadfoot;

The coils are Continuous Duty and I have used many 110 VAC as safety valves so when the E-Stop is hit it dumps pump flow and opens the circuit to tank. However, this is usually with Mineral Oil not Water Glycol.

My question was and still is does heating have anything to do with whether it is AC, DC 12 Volts 440 Volts or anything in between. Is there a best way to power a Continuous Duty Solenoid on a hydraulic control valve?

The coil like all electrical parts do have temperature ranges. Usually for industrial applications they are rated 40C or 104F as ambient.

I have seen many different votages and have not seen one that heats more or less than others. Coils are like transformers, and are wound for specific applications and power needs. You may need some that are designed for higher temps.

Just out of curiosity what is the temp of the fluid running thru the valve normally?

I am having a problem figuring out exactly what the valve does

This is a strange valve. What is the integral adjustment? You would think that there would be a small pilot circuit so the oil can hold the valve in the correct position instead of relying on the solenoid alone.

When I get home I will look at the example in your book.


It makes no difference what it does, just how much energy it dissipates. If you look at your electrical specifications on page 30 you can see that the 24v solenoids take over twice as much power as the low watt AC version. Even so, I don't see how 41 watts is going to make a big difference on a hydraulic system. It seems to me that most of the heat will be generated by the hydraulic system itself.

Bud I am going to jump in here before it gets too technical and still doesnt answer your question.

Using the info on page 30 you can see the coils will use approximately 30-40 watts (depending)of power, a side effect with any coil will be some heat BUT environment, the system, etc can ADD to that effect (accumulative) and become hotter...ie if the valve is directly controlling a fluid with temperature at 200° F then you will probably get some transfer heat to the coil.


Heat...watch this word...FLOWS between regions that are not of thermal equilibrium...sound familiar?


The answer to your question is NO, the voltage has no bearing on the amount of heat dissipated by the coil. It can have a bearing on current used in the system, as you can see a 24vdc coil will need more current than a 120vac coil, this just has a bearing on circuit design though.

Bud,

Ron is absolutely correct. The number to look at to get an idea of the heat generated by a solenoid is Watts, or Volts multiplied by the current (Amps). It is not the voltage rating or the current rating or AC versus DC, but the volts X current that determines how much heat is generated.

Leadfoot;

I always figure a well designed hydraulic circuit will operate at a temp of 5-15 Deg. F. above ambient. That often means adding heat in cold weather but seldom requires any cooling. This of course is a typical Bang-Bang circuit not a Proportional or Servo valve circuit.

The only thing besides outside influences that make a hydraulic circuit run hot is WASTED EENRGY. Actually the same as an electrical circuit.

Peter;
You can also look at the Power Point presentation on Relief Valves. It may be a little easier to understand the function of a Solenoid Opearted Relief Valve by seeing it in color and in a typical Run/Stop circuit on Slide 32. There is a link of an animation on Slide 32.

Thanks all for answering my question. I now know how to determine if a manufacturers coils will run hot even though they say Continuous Duty.