Advice on Regulator Selection for Foundry Furnace

[vtcnc]

My father scored a free foundry furnace, blower and tube from a friend. Well, o.k., not free - he traded a couple of game skulls for it.

Anyhoo...the prior owner claims it was hooked up to a LNG line from his shop. I plan to fire on LP. I have the steel jacketed flex line that tees into the blower tube. There is no nozzle or regulator for the atomization and control of propane.

There is plenty out there on nozzles, blower tube, etc., but I'm having a hard time nailing down the type of regulator I should purchase. One thing I have learned is that a grill regulator will not work, the pressure is too low. Please correct me if I have drawn the wrong conclusion on that point.

I found this one from a link source on backyard foundry:

Amazon.com : GasSaf 5FT 0-10PSI High Pressure Propane Adjustable Regulator with Hose or QCC1/Type1 Propane Tank Cylinder Fits for Turkey Fryer,BBQ Grill, Heater, Stove and More Appliances -Safety Certified … : Patio, Lawn & Garden

Amazon.com : GasSaf 5FT 0-10PSI High Pressure Propane Adjustable Regulator with Hose or QCC1/Type1 Propane Tank Cylinder Fits for Turkey Fryer,BBQ Grill, Heater, Stove and More Appliances -Safety Certified … : Patio, Lawn & Garden

www.amazon.com

This claims to be high pressure, but as I inevitably shop around, I see other regulators for upto 20, 30 and 60! psi.

So, the furnace will only be suitable for small crucibles, maybe no more than 3# of aluminum. Any advice on what size and type of regulator I should be looking at?

Thanks

 

[jwmelvin]

With forced air, I don’t see why you’d need high propane pressure, because you can use as large a jet as you like. (In my naturally aspirated forge, the small jet creates a high-velocity propane stream to entrain air (Venturi effect).) So while a naturally aspirated burner may require up to about 20 psi, I see little chance for that with a blown burner. And a 0-10 psi regulator may give you better control in the range you need.

 

[vtcnc]

With forced air, I don’t see why you’d need high propane pressure, because you can use as large a jet as you like. (In my naturally aspirated forge, the small jet creates a high-velocity propane stream to entrain air (Venturi effect).) So while a naturally aspirated burner may require up to about 20 psi, I see little chance for that with a blown burner. And a 0-10 psi regulator may give you better control in the range you need.

OK, just so I can confirm I understand, in the case of naturally aspirated burners, the regulator must supply enough gas at pressure to get to necessary heat?

And conversely, a forced air system will compensate for the low pressure regulator? Am I understanding correctly?

EDIT: it seems like the control then would have to be on the blower so as to achieve an adequate flame. Correct?

 

[jwmelvin]

Looking on Amazon, it seems the 0-20 and 0-30 regulators are more plentiful. I’d just get one of those and go for it.

 

[jwmelvin]

OK, just so I can confirm I understand, in the case of naturally aspirated burners, the regulator must supply enough gas at pressure to get to necessary heat?

And conversely, a forced air system will compensate for the low pressure regulator? Am I understanding correctly?

EDIT: it seems like the control then would have to be on the blower so as to achieve an adequate flame. Correct?

With naturally aspirated, you need the pressure to drive a small stream of propane through the jet. With a blown system, you aren’t relying on the propane flow for your air flow (the blower does that) so the propane pressure does not need to be so high.

In either case, it’s important to control the air:fuel ratio. For propane, that’s ~15.7:1 for optimum combustion (stoichiometric). You will control that with the blower speed, blower restriction, propane pressure, and propane restriction. Lots of ways to do it. Your overall heat power input will depend on propane flow and mix ratio. Since you want efficient combustion, let’s say you will tune for stoichiometric mix.

To get the most power (highest rate of heat input), you will run the blower wide open. That delivers a certain amount of air. Now you need propane to match, so you will adjust the regulator pressure to deliver the right amount of propane. If your jet (restrictor on the end of the propane line) is too small, even with the regulator maxed out, you won’t get enough propane. But there’s no need for a small jet in your case, so by balancing the jet size against regulator pressure, you can achieve the propane flow necessary to get the stoichiometric mix you want with full blower output. That will be the maximum heating power for your forge. If you want less heating power, you will reduce airflow and propane flow proportionally (by blocking off the blower and reducing propane pressure).

 

[vtcnc]

With naturally aspirated, you need the pressure to drive a small stream of propane through the jet. With a blown system, you aren’t relying on the propane flow for your air flow (the blower does that) so the propane pressure does not need to be so high.

In either case, it’s important to control the air:fuel ratio. For propane, that’s ~15.7:1 for optimum combustion (stoichiometric). You will control that with the blower speed, blower restriction, propane pressure, and propane restriction. Lots of ways to do it. Your overall heat power input will depend on propane flow and mix ratio. Since you want efficient combustion, let’s say you will tune for stoichiometric mix.

To get the most power (highest rate of heat input), you will run the blower wide open. That delivers a certain amount of air. Now you need propane to match, so you will adjust the regulator pressure to deliver the right amount of propane. If your jet (restrictor on the end of the propane line) is too small, even with the regulator maxed out, you won’t get enough propane. But there’s no need for a small jet in your case, so by balancing the jet size against regulator pressure, you can achieve the propane flow necessary to get the stoichiometric mix you want with full blower output. That will be the maximum heating power for your forge. If you want less heating power, you will reduce airflow and propane flow proportionally (by blocking off the blower and reducing propane pressure).

This all makes sense. Thanks. I'll post pics of what I have and what the results are once I piece it all together.

 

[pontiac428]

How many BTUs/hr will you need to melt 3 lbs of beer cans? That seems like the key to me. Gas volume can be throttled with a critical orifice after the regulator diaphragm valve. Most of them are rated by max thermal capacity in BTU/hr. That should be easy info to find to produce your melt.

 

[ericc]

OK, just so I can confirm I understand, in the case of naturally aspirated burners, the regulator must supply enough gas at pressure to get to necessary heat?

And conversely, a forced air system will compensate for the low pressure regulator? Am I understanding correctly?

EDIT: it seems like the control then would have to be on the blower so as to achieve an adequate flame. Correct?

Hi vtcnc. Correct on both points. A blown burner will usually have just a simple tube for the gas. These are typically fed at very low pressure, under a psi. The natural gas line in a home runs at a similar low pressure. The 0-10 psi or greater are for venturi (self aspirating) burners, like the Reil burner or Frosty burner. The higher pressure propane regulators are often repurposed from turkey fryers and they are often color-coded red. The silver colored BBQ regulators that you can get at a big box store should provide a decent pressure unless the furnace is really large. For example, a Johnson forge eats gas and may draw too much for a BBQ tank. Unless you have a large setup, it is more economical to have a smaller burner, since it can eat the cost of the unit in tank refill charges.

 

[rwm]

I use a squirrel cage blower on a Reil type burner. I just switched from a 30 PSI to a 60 PSI regulator so I could get more BTUs. This makes a big difference when melting brass/bronze. For small aluminum melts a 30 PSI regulator is fine.
BTW there are people who just use the tank pressure and a needle valve and then adjust the flow to optimize combustion. That works too.

 

[Cadillac]

I use a acetylene regulator I had and the line from a O/A setup. I had some old ones. Then at the business end I have another ball valve for volume control. Instead of a blower I use a airline from the compressor. The air line also has a regulator on it which if I remember I inject about 5-10 psi of air. I’m sure theirs better ways but it was all material on hand. Works good.