Remember these questions from last time and did you find the answers?
What are the flow rates for most pipe sizes that would be used on a fresh water (potable) feed to a steam boiler, specifically ½” and ¾” pipe and at a working pressure of 55-60 psi? What is the average water content of a typical four section steam boiler for oil (about 135,000 Btus? How about the same boiler for gas?
The answer to the first question is that with a ½” pipe you can flow about 10 gallons per minute (gpm) and at ¾” you can flow about 16 gpm, that’s forced pressurized flow, not heat transfer flow. The answer to the second question is that a typical 4 section, residential, steam, oil boiler, Figure 5-1, holds about 12 gallons of water to the “working water line” and gas, steam boilers, Figure 5-2, hold about 9 gallons of water.
Now another couple of other questions? How long will it take at 10 gpm to fill an empty boiler to the working water line? In either case you’re talking, at full flow, the ability to fill either boiler in about a minute and that’s from empty! How long does it take to put in a gallon or two, well about 6 to 12 seconds, right?
So now we go back to the dilemmas. How do you fill that boiler slowly and how do you protect the boiler from overfilling both manually and automatically? As to the manual side we’ll take a look at something you’ve probably worked on and wondered about. Have you noticed that an awful lot of automatic water feeders for steam out there have 3/8” tappings, Figure 5-3? Those 3/8” valves have a very definite purpose, to control flow. You see a 3/8” pipe only has a flow rate of 6 gpm at 55-60 psi, but a ¼” pipe only has a flow of 3 gpm at the same pressure. Ever have an older customer or someone with arthritis or other problem where opening and closing a globe or gate valve made refilling the boiler a big deal? Remember how good you felt by just putting on a ball valve for them? You looked like a hero because it was so much easier. Back in the day we all converted a bunch of people from the infamous #14 blow down valve to a ball valve using a “dirt pocket cap” and a nipple, today most just use something like the #14B valve, Figure 5-4. So, no doubt about it everyone loves the ball valve, Figure 5-5. It’s perfect for where you want a full open or full close valve and for drains or feeds the mighty valve ball is it! Now the trick is to use a ¼” ball valve instead of the usual ½” or ¾” size valve, Figure 5-5, with reducers, Figure 5-6. By doing that you limit, on a ½” system, the flow to just 3gpm. That’s easier on the boiler and customer and greatly reduces shocking a hot boiler with really cold water in the winter. In addition, it makes it a lot harder for anyone to overfill the boiler quickly.
Finally, I’ll bring back a couple of characters everyone seemed to enjoy and relate to so here’s a memory with Bruce & Bubba from 1995. This has been one of our most requested articles.
Here’s the story.
Recently one of ‘Friendly Oil’s’ customers had a boiler replaced.
The installers put in a new steam boiler, adjusted all the controls, did a combustion test, and then left.
In the next three days they got seven service calls for erratic and insufficient heat.
After several of the oil company burnermen (hmmm), walk in, find the unit hot, the burner capable of running, and nothing wrong, the service manager gets steamed!
In desperation, the service manager of ‘Friendly’s’ decides to get another opinion, and so he calls his old buddy Bruce.
But Bruce is very busy with a commercial burner problem and so he decides to send one of his techs, but this is not just another burnerman walking in, no way, it’s Bubba and boy has he learned since we last met him. He now knows that the second Rule of burner service is ‘assume nothing’, and that the first Rule is ‘listen to the customer’.
After he arrives and gets in, here’s what happens.
“Hi there, I guess you’re having a problem with your new boiler”, asks Bubba.
“A problem, oh yeah, we’re having a problem all right”, says the customer, Mrs. Nastybear, “we spend three thousand dollars (1995) for a new boiler, and it works best when the burner is off, and now they send another guy!”
“When the burner is off”, questions Bubba, “please explain what you mean.”
“Wow, now there’s the first change”, says Mrs. Nastybear, “he just doesn’t want to go down the basement, okay here is what happens. We have a clock thermostat because we both work, we like it cool at night, and we’re still trying to save money (some things never change). After the heater has been off for a while and it first warms up, it heats fast, and the radiators start to get hot.
Then the radiators don’t get any warmer, and the burner keeps running. Then the burner shuts off, and then just when the radiators start to warm up again, the burner comes on and the radiators don’t get any hotter. Just like I said, it’s better with the burner off”.
“I think I know what to do”, says Bubba, “let me have a look at it.”
After being in the basement for some time, Bubba comes up and announces to Mrs. Nastybear that he has replaced a control, made some adjustments, and now feels the problem is fixed.
Do you know what control Bubba changed, and what adjustments he made? And why did the radiators act this peculiar way?
Well, here’s the story he told Bruce, so let’s see what happened.
“I arrived at the job Uncle Bruce, listened to the customer tell her story and replaced the new existing pressure control, Figure 1. It was running way over three pounds before it shut off, and I couldn’t get it to run the burner the way you showed me. I put on a vapor type control, Figure 2, and set it to shut off (cut-out) the burner at 16 ounces and to cut the burner back in (cut-in) at four ounces. The radiators got nice and hot, and the customer seemed happy”, explained Bubba.
“Well, I’m glad you remembered what I told you about pressures, and did all of the air vents work”, asked Bruce.
“Boy, I think so,” replied Bubba, “because you told me that at 1-1/2 psi those vents, Figure 3, are supposed to close, and all of them did, they wouldn’t let any more air out, and so no more steam came in, just like she said, ‘it worked better when the burner was off”. But my question is why does the vapor control work so much better?”
“It has to do with pressure and in this case, size does matter”, replies Bruce. “See that small round thing just above the brass fitting, Figure 1? That’s where the diaphragm that operates the control is. Internally it’s about the size of a silver dollar. Now on the vapor control it’s about the size of a cup saucer, big difference and why the vapor control just works better because it reacts to the steam vapor better. I guess I better call Friendly’s and tell them the news, and then bill them for the call and the control”, said Bruce. “They will have a fit over the price of that vapor control, but if they had put one on with the boiler, they could have saved themselves eight service calls, oh well.”
Did you figure this one out for yourself?
Remember these important facts:
1) The #1 air vent, Figure 4, or its equivalent, Figure 3, were designed to run at a maximum of 1-1/2 psi, and if you go over that they do their job and shut down. It’s called drop away pressure, Figure 5.
2) Normal pressure controls have minimum operating ranges of .5 psi to 1.5 psi and may not be sensitive enough to work with many systems with new faster steaming boilers.
3) Vapor controls run on ounces, and the correct one for residential should have a maximum operating pressure of 1 psi (16 ounces).
4) Most, if not all, residential steam systems ever designed were laid out for an operating maximum pressure of two psi.
5) Any control, regardless of price, is cheaper than repeat calls.
This is a common problem, and so I have to keep wondering when everybody will put on the right control to begin with? Don’t think that all you have to do is up the capacity of the air vents either. If you do, you will create even bigger problems. What problems you ask, well, how about problems with ‘water hammer’, condensate return, and if an automatic feeder is present, flooding of the boiler. Take the easy way out, put on a vapor control. lFON
George Lanthier is the owner of Firedragon Academy (www.FiredragonEnt.com), a 35-year-old Massachusetts Certified School teaching gas, oil and other heating subjects. The Academy has its training facility in Webster, Massachusetts. Lanthier is the author of more than 60 books and manuals on HVAC subjects, published by Firedragon. Lanthier is a CETP, ESCO, NATE, NORA, PMAA and PMEF Proctor and has been a Massachusetts Certified Instructor since 1975.