Steam Pressure Regulating Valves

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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cyberbadger
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Steam Pressure Regulating Valves

Post by cyberbadger » Fri Jul 10, 2020 2:48 pm

On a recent outing in June we ran Nyitra on a combination of propane, kerosene, and some wood.

The 2.5mm steam atomizer worked ok, but it was finicky. As the boiler pressure changed it would require adjustment.

I saw a recent post by RNoe where part of the oil atomizing rig appears to have some kind of pressure regulator/compensator - the green dome in the pictures. viewtopic.php?f=4&p=19789#p19789

I've ordered one of these from McMaster Carr, but there is a 3 week leadtime.

Extended-Life Pressure-Regulating Valves for Steam
Max Steam Pressure: 250psi
Steam Output Range: 40-110PSI
Temperature Range: -20° to 400° F
"For a longer service life than cast iron valves, these have a durable bronze body. All automatically reduce a high, variable inlet pressure to a lower, stable outlet pressure. Adjust the outlet pressure within the range. Valves have an internal strainer to trap debris."
steampressurereg.png
steampressurereg.png (32.94 KiB) Viewed 929 times
As much as I'd love to always be at 200PSI, operationally the boiler pressure can vary between 100psi-200psi depending on what is going on.

Anyone have any tips on using such devices, especially for oil atomization?

I plan to put the needle valve after the pressure regulator, and probably some kind of valve there to cleanout the condensation during startup. I hope I don't need to get a steam trap too....

Also what is the typically required drop in pressure in such devices? Say if I want the output to be 100psi, what is the minimum input steam psi input? 120psi?

-CB
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fredrosse
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Re: Steam Pressure Regulating Valves

Post by fredrosse » Sat Jul 18, 2020 12:01 pm

"I plan to put the needle valve after the pressure regulator, and probably some kind of valve there to cleanout the condensation during startup. I hope I don't need to get a steam trap too...."

At very small steam flow, appropriate for a steam atomized oil burner, condensate accumulation both downstream and upstream of the regulator may occur. Insulate all of this piping to minimize condensate. Purging condensate just upstream of your new regulator may be required, (some regulators get finnikey with small flows and wet steam inlet) and a small needle valve (or steam trap) will do this. For the outlet of the regulator, another small needle valve (or steam trap) just before the burner needle valve may also be required for startup.

Note that some regulators are not happy with a very small steam space volume on the outlet (regulator outlet to burner needle valve contained steam volume). The regulator may "hunt", giving continuously variable outlet pressure, which is exactly the problem you are trying to solve. To avoid this possibility you may require some added volume, perhaps a few (or several) cubic inches contained volume, but you may not require any added volume if the regulator is well behaved and stable.

Downstream of the burner needle valve I assume you will have some stainless steel tubing in the firebox to provide good superheat at the inlet to the oil atomizer. Oil atomizers are famous for giving trouble if the inlet steam is wet.

"Also what is the typically required drop in pressure in such devices? Say if I want the output to be 100psi, what is the minimum input steam psi input? 120psi? "

The answer to this question depends very much on the regulator design/sizing, compared to the steam mass flow while in service. Your guess of 120 PSI is probably reasonable, but it is just a guess unless you know your steam mass flow and can get the technical details of the regulator. As an extreme example, a 1/4 inch regulator may work OK, but need 50 psi overpressure (Pressure above the controlled pressure), but if you bought a 2 inch regulator it might work with only 1 PSI overpressure, but would need a few cubic feet of downstream volume to operate in any way with stable outlet pressure. Having worked with all kinds of fluid systems in the steam power industry for over 45 years, I have often seen these kinds of design problems causing plant delays and much gnashing of teeth.
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Re: Steam Pressure Regulating Valves

Post by cyberbadger » Sun Jul 19, 2020 2:35 pm

Fred,

The exact one I have ordered is this model
McMasterCarr Catalog #: 47345K32 - 40 to 110psi model
https://www.mcmaster.com/47345K32/

It is 3/8" npt inlet and outlet. My thinking behind this it might be able to support up to two atomizing nozzles in the future.

Right now I have one nozzle and about two feet of 1/4" braided stainless "extreme temperature" hose.

When I took Nyitra out in June I generally started by closing the fuel, and running the nozzle to let any condensation get through, then opening the fuel valve and letting fuel be sucked in.

I will watch for condensation, my perception was that as the boiler pressure increased without changing the steam atomizing needle valve, the kerosene atomizing would start blowing itself out.

I have thought about some kind of flame holder, I see examples of flame holders, but the best flame holder I have tried was to throw a sheetmetal fireplace shovel into the firebox as a target for the flame.

Current Atomizer configuration used recently. 1/2" schedule 80 steel, 2 Apollo Class 250 ball valves, brass no-shok needlevalve, braided extreme temp stainless steel to the nozzle. (The redline I put in the picture below)

This picture is with the burner out of the firebox - you push it about a foot and it is roughly in the center of the bottom of the ashpan.

Image

-CB
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Re: Steam Pressure Regulating Valves

Post by fredrosse » Mon Jul 20, 2020 1:50 pm

McMaster sent me the technical data for the regulator, but what is the actual burner steam flow, and at what inlet pressure you need at the burner steam inlet? That is the data needed to complete the review of the valve sizing.

If you do not know the steam flow to your burner, could you give details, such as the steam orifice diameter (or steam slot size, or other details? A detailed drawing would be best if you have that.

I am largely in semi-retirement now, but want to keep my engineering of fluid systems intact.
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Re: Steam Pressure Regulating Valves

Post by cyberbadger » Mon Jul 20, 2020 3:08 pm

This is the thread for the 2.5mm nozzle I am using: viewtopic.php?f=8&t=2274

The 2.5mm nozzle is made of brass and stainless steel. The center bore is 2.5mm. It was designed for air, I replaced the O-ring with a steam rated Viton O-ring.
Heavy Oil Waste Oil Alcohol-based Fuel Burner Nozzle 1mm 1.3mm 1.5mm 2mm 2.5mm

Material: Brass
Out Diameter: 17 mm
Total Length: 67 mm
Oil Inlet: 3 mm(1/8")
Air Inlet: 6 mm(1/4")
Bore Diameter: 2.5mm
Working Pressure: 0.03~0.04Mpa
NozzleOil.png
NozzleOil.png (503.2 KiB) Viewed 722 times
I've only run it a few times, but I have run on propane until I got 50psi steam.

That seemed enough to get the steam atomizing nozzle started.

Operationally Nyitra's boiler MAWP is 200psi. Underway boiler PSI can vary between 100-200psi.

The nozzle steam consumption is almost nothing on the water glass.

The 1/2" Apollo ball Valves have a Cv of 15.

The 1/4" No-Shok Brass 102-FFB Needle Valve has a Cv of 0.42 and an orifice size of 0.172".

I also just received a Dwyer stainless steel 1/4" Needle Valve HNV-SSS32B. Unfortunately the Cv is not available for this but it is definitely not full port.
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Re: Steam Pressure Regulating Valves

Post by barts » Tue Jul 21, 2020 8:04 pm

I made my own regulator from a standard gas (oxy?) pressure regulator and a reach rod & remote valve (stainless ball in a tee) for Otter, following Allan Gregg's design.

I wrote this up in steamboating iirc; I'm in WA so don't have the details handy.

- Bart
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Bart Smaalders http://smaalders.net/barts Menlo Park, CA
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