Pressuretrol setting with over capacity boiler

SteamingatMohawk

I have Smith boiler with at 133000 BTU/HR capacity and total radiator ratings add to about 79000 BTU/HR. Some of the original radiators are no longer installed, hence the mismatch. MY boiler cycles on the pressuretrol at 2psig cut-out, 0.5psig cut-in. It seems to me I could reduce the cut-out to 1.5 psi (1.0 psi differential) and save some money.

ethicalpaul

Yes, you should. And make sure your main venting is in good shape, that is critical.

mikeg2015

Does it build pressure before all radiators are heated and cycle then? Or only after everything is fully heated? Is this 2 pipe or one pipe system?

SOme boilers have dual firing rates, or with a combustion analysis, could be possible to down fire it, or use a 2 stage gas valve tied to a second pressure control.

Residential systems shouldn’t t really build any pressure. Building pressure is usually due to to slow main venting or undersized header and laterals compared to the total steam capacity. But depends on the type of system.

Jamie Hall

ethicalpaul said:

Yes, you should. And make sure your main venting is in good shape, that is critical.

This^^^. You may not save much money -- though you may save some -- but the poor thing is going to cycle pretty much no matter what you do. That said, if all the radiators get warm enough, you could also set your thermostat to 2 cycles per hour instead of 1 (if it allows that) and see if that helps.

dopey27177

Pressure control settings are for the operation of the system not to save money because of possible short cycling.

Your best bet is if you have an oil burner is to change the nozzle in the burner to a lower fire condition.

You can use safely a nozzle of 1/3 the nozzle size you are using now. That can save you money.

How much you save depends on the boiler run time with the smaller nozzle.

Jake

Jamie Hall

That is, you can downfire as @dopey27177 suggested if, and only if, the burner and boiler configuration is tested for the lower firing rate, and a fully competent technician sets up the nozzle and the combustion parameters.

Otherwise, you are engaging in experimental engineering...

SteamingatMohawk

I have the Honeywell wireless thermostat with WIFI capability. I'm not sure what CPH is set, but I have a vague recollection there is a choice of steam in the menu. I'll check it out. Thanks for the suggestion.

Single pipe steam, it trips on the pressuretrol if the heat hasn't been on for a while, like on a warm day which we have had where I live in upstate NY. The boiler comes back on after the pressure lowers to the cut-in point as long as the thermostat is still calling for heat. It seems like reducing the cut out will just reduce the time between cut-out and cut-in while the system still wants heat.

If you look at my other discussions, you can read about all the different things I have done over the past couple of years. Too long a story to repeat here. Lots of learning and great help from the guys on this website.

dopey27177

Type O

I said use a nozzle 1/3 the size of the existing nozzle. MEANT 2/3 THE SIZE OF THE EXISTING NOZZLE.

Jake

Jamie Hall

May I say it in a different way? Somewhere in the literature on your specific boiler there will be a section on the tested firing rates for that particular boiler. You can, with the aid of a competent technician, vary the firing rate within that range by changing the nozzle to the appropriate one and adjusting the air shutters, oil pressure, sometimes blast tube and other settings, and the draught. This can only be done with the aid of the appropriate test instruments used by someone who knows how to use them.

Attempting to adjust the firing rate outside of that range is strictly experimental and would be entirely at your own risk, and often will not give the results you might expect -- such as reduced fuel use. You might find a technician willing to help you try it -- but if it doesn't work, remember it's your puppy now.

SteamingatMohawk

Thanks for the suggestions, but I should have mentioned my boiler is gas fired.

I could do radical things like installing smaller orifices or plugging 2 of the 5 burners. Neither option is appealing to me. I have no clue as to how much smaller the orifices could/should be and plugging the two end burners would make a significant change in the heat distribution in the fire chamber.

I can't imagine any local contractor recommending either alternative. The one I used most recently told me there was a leak in the boiler because the flame was yellow. After reading some of the discussions and literature on boilers, then inspecting the flame, I found out the dust on the floor was causing the yellow flame. Once I bent down to observe the flame, if I stayed still for at least a minute, the yellow went away. So much for that recommendation.

Jamie Hall

Actually, gas boilers can be downfired, too, although the procedure is somewhat different. And no less tricky to get right. Same precautions apply. And you are quite right -- just closing off a burner or two just isn't going to make either you or the boiler a bit happy.

EBEBRATT-Ed

@SteamingatMohawk

Playing with the pressure control will just cause more rapid short cycling if you lower the pressure. Make sure all the venting is up to snuff.

If it is an atmospheric gas boiler the gas manifold pressure is probably set to 3.5" wc. You can probably lower it to 3" wc but only after testing with combustion instruments.

SteamingatMohawk

Yes, and I have a Yellow Jacket manometer to measure the gas pressure. The company I mentioned above had two different guys at the house a day apart and either the guys didn't know how to use the instruments or one or both of their instruments was seriously out of calibration.

I found a manometer on the internet that's a tube within a tube, not a u tube manometer. It's a bit confusing how it works, but it does. See the pic. I believe it before I believe the electronics.



I don't have a problem with short cycling at the lower pressure, since many of the discussions consistently mention the lower the pressure the better. It could be a tossup between short cycling at the higher pressure with more time to dissipate the energy at the radiators vs. short cycling at the lower pressure and less time to dissipate the energy. For 0.5 psi difference between the two, it may not even be easily observable.

I tend to think the lower number of radiators (heat dissipation capacity) makes it more difficult for the system to transfer the heat as fast as the boiler produces it. That being said, once all the air is gone, it's just a matter of time for the radiators to dissipate the trapped heat that hasn't made it to the radiators.

While I did do some calculations to determine the radiator capacity, I haven't tried to calculate the required vent rates to expel all the air from the system simultaneously at all radiators. I know I can do it in a spreadsheet, but I haven't tried to wrap my brain around the equations.

Finally, since I did the balancing act a year ago and put the thermostat in the coldest room, I don't have complaints about heat. So, I am not too inclined to mess around with the individual radiators. It's a 90 year old house converted from 2 apartments to 4 and each apartment behaves differently and each tenant has their own preferences.

Jamie Hall

on the venting...

If It Ain't Broke, Don't Fix It

SteamingatMohawk

Yes, Yes, Yes. My sentiments exactly.

dopey27177

Your gas company has qualified technicians to lower the firing rate of the burner. Give them a try. Many gas companies out source some of the work to companies that employ qualified technicians.

As far as saving fuel goes some time you win and some time there is no money saved.

Where you win is short cycling goes away and you can operate at lower steam pressure.

Operating at lower steam pressure will make the vent valves quieter and more efficiently.

Jake

SteamingatMohawk

Agreed. With lots of swapping around vent valves and orifices and main vents and moving the thermostat to the coldest room, I came up with a configuration that is working reasonably well...proof is no complaints from the tenants.

My next steps are to improve the overall situation without messing it up. That being said, reducing the cut out point from 2psig to 1.5psig on the pressuretrol is simple both physically and technically.

The next is to determine if I can be successful in increasing the main venting. The house has two headers, one is 25 feet long before it turns into the return and the other is 15 feet before it turns into a return. There is one Gorton #1 at the end of each return where the returns turn down to the Hartford loop. In addition, the 25 foot main has a Gorton#2 at the point where the main turns back to be the return. I have a leftover Gorton #2 and am speculating if replacing the #1s with #2s ( and leaving the existing #2 in place) would speed up the main venting without messing up the individual radiator venting. I have a vague recollection that when I did try the #2s on the return, it didn't make a difference. But I changed out all but one of the radiator vent valves from Heat Timers to Vent Rites and MoMs and don't have detailed records of what was where when.

gfrbrookline

Are the rooms coming off the 15' main cooler than the rooms on the 25' main? Do both mains fill with steam at about the same time?

gfrbrookline

With all of the experiments I did with my main venting I found that in my case, every system is different, the main venting determination was based on both the diameter and length of the main plus the size of the radiators connected to the main.

I have 2 mains, both 2" and 75' long. One serves 75 percent of the connected load so I adjusted my main venting accordingly, didn't read that in a book just went on intuition and got it right. I have 6 big mouths/ 3 each on 2 dry returns on the main that carries the load and 2 gortons #2's and 1 gorton #2 on the dry returns on the main with the light load. I have 4 returns because my building is stepped on a hill.

With this configuration the mains all heat at the same time and the radiators also see steam evenly. The temperature in each unit is within 1 degree so we are well balanced. The radiator venting is based on the Gill/Pajek formula with gortons.

SteamingatMohawk

The longer main serves 5 radiators, the shorter one serves 4. It appears they work pretty well together, except when the tenant who has the thermostat does a lot of cooking on a cold night. The thermostat is a bit close to the stove, even though it is in an adjacent room. When that happened, I had her move it to a different location, which seems to have solved the problem. It was easy, because I had installed a Honeywell wireless thermostat with WIFI, so there are no wires to disconnect. And now I don't have to leave the basement if I want to exercise the system, I just use the app on my phone. $300, but it was worth it.

gfrbrookline

I would try putting the G2 on the 15' main and add the G1 to the existing G2 on the longer main and see how everything responds. Better to vent the system through the mains than the radiators.

I have a VisionPro that does the same, love it.

SteamingatMohawk

I apologize, I don't think I described the arrangement well enough. Hopefully you can read the attached file. All three Gortons are on tees with the vent above the pipe. It's hard to show that in 2 dimensions. This should help.

Hap_Hazzard

For those who don't have powerpoint,

SteamingatMohawk

Thanks. How did you convert it?

Hap_Hazzard

From powerpoint, choose File > Export and save it as png or gif.

SteamingatMohawk

@Jamie Hall On 1/25 you mentioned the CPH. I checked and the tstat controller is set for "steam or gravity" at 1CPH, so that's OK.

SteamingatMohawk

Thanks, I also found I can print to .pdf.

SteamingatMohawk

@gfrbrookline Last night I did the Gill/Pajek calculations for main venting and was surprised that the Gorton#1s are the right size. I couldn't believe it, so I even redid my calculations to make sure I didn't make an error. They have enough capability to handle my "small" system.

Like it was said elsewhere, if it ain't broke don't fix it. If I do find some reason to make a change I will revisit your suggestions.

SteamingatMohawk

At the very beginning of this discussion, I mentioned my Pressuretrol settings. Today I checked them while the boiler was running. It cut out at 2.0 psig and back in at 1.0 psig. The Pressuretrol is set at 0.5 psig (minimum) cut-in and 1.0 differential. I turned the adjusting screw to make sure the indicator was all the way down to try to lower the cut-in, but by inspection, it didn't seem to do anything. Has anyone experienced this situation, namely that the lowest cut-in is higher than 0.5 psig. The Pressuretrol is 20 years old and works, just not at the correct cut-in.

Jamie Hall

Not at all unusual. There is a way to calibrate them around here on the Wall somewhere...

Precaud

I basically copied @Gordo 's setup to calibrate mine:

https://youtube.com/watch?v=mE1-QuUx4_c

If yours is the version that has the larger diaphragm, you should be able to adjust it to 1.5 lbs cutout and .5 lbs cutin easily. The smaller-diaphragm one will cut out well but the cut-in point is less accurate and less repeatable.

SteamingatMohawk

The problem is that I am unable to adjust the cut-in any lower than 1.0 psig even with the indicator at the 0.5 psig point. Could there be some thing restricting the mechanism from going lower? I haven't seen anything obvious that could be hanging it up.

Precaud

Which model Ptrol do you have?

ethicalpaul

a

SteamingatMohawk said:

The problem is that I am unable to adjust the cut-in any lower than 1.0 psig even with the indicator at the 0.5 psig point. Could there be some thing restricting the mechanism from going lower? I haven't seen anything obvious that could be hanging it up.

It's just the way they built it. Mine is exactly the same way. You can try the calibration that @Fred shared: https://forum.heatinghelp.com/discussion/149944/i-figured-out-how-to-calibrate-a-pressuretrol

I once modified mine in a way that made it run perfectly but wasn't advisable.

But for anyone who is continually cycling on pressure even with good main venting and doing everything reasonable to reduce the capacity of the boiler, I would strongly recommend a delay relay that will give the boiler a "time out" for 10 or 15 minutes after it first reaches the pressure limit.

This lets the heat leave the radiators for awhile without wastefully burning fuel

SteamingatMohawk

The Pressuretrol is a PA404A. The calibration videos don't deal with a minimum setting for the cut-in of 0.5psig, but actual cut-in of 1.0. I've had this boiler for 20+ years and never paid any attention to the actual cut-in compared to the setting of the adjustment screw.

Fred

SteamingatMohawk said:

The Pressuretrol is a PA404A. The calibration videos don't deal with a minimum setting for the cut-in of 0.5psig, but actual cut-in of 1.0. I've had this boiler for 20+ years and never paid any attention to the actual cut-in compared to the setting of the adjustment screw.

Calibrating the "Cut-Out" pressure also calibrates to Cut-In by changing the amount of tension on the spring. Follow the procedure that @ethicalpaul posted above.

SteamingatMohawk

@Fred I respectfully disagree with your statement. The Cut-in is set by the screw/spring arrangement establishing the position of the switch for it to make contact. The differential sets the amount of pressure increase (i.e., movement) for the switch to be allowed to open. They are independent.

Regardless, the problem was stated above as the lowest setting for the Cut-in does not establish a true trip point of 0.5 psig.

@ethicalpaul said "I once modified mine in a way that made it run perfectly but wasn't advisable." I can only guess it had to do with changing the way the Cut-in spring, etc. interact.

Elsewhere, I think it was on this site, I found a comment that someone had done something "unusual" and ended up with a situation where the switch would not Cut-in at all and ended up with no heat, once the pressure went high enough for the Cut-out to trip the switch off.

I'm trying to connect with Honeywell to see what, if anything, they have done to remedy this situation, since I have the impression Pressuretrols can be finicky.

Hap_Hazzard

SteamingatMohawk said:

@Fred I respectfully disagree with your statement. The Cut-in is set by the screw/spring arrangement establishing the position of the switch for it to make contact. The differential sets the amount of pressure increase (i.e., movement) for the switch to be allowed to open. They are independent.

You're 50% right. You can adjust the cut-out without changing the cut-in, but you can't change the cut-in without changing the cut-out by the same amount, so they're not fully independent. They are additive..

The main scale set-point screw changes the spring pressure on the rocker assembly, which varies the amount of pressure required to open and close the switch, increasing or decreasing the cut-in and cut-out points by the same amount. The differential setting changes the contact position inside the microswitch, which varies the distance the actuator needs to travel before the contacts open, so only the cut out point is affected and is equal to the sum of these two adjustments.

If the pressure differential between cut-out and cut-in is not equal to the number indicated by the position of the thumbwheel, the switch is bad. If the cut-in is not equal to the pressure indicated by the main scale set-point, the rocker geometry is incorrect. This can be adjusted, using a 0.05" (50 thousandths of an inch) hex key.

Remove the cover from the Pressuretrol and find the grub screw on the rocker assembly (circled in the picture below).

There will be some lock-paint on the grub screw, but it can usually be freed up by turning the screw counter-clockwise to break the lock-paint. Return the screw to its original position before adjusting. If the screw can't be turned, try chipping the lockpaint with the point of a, X-acto knife.

If the cut-out pressure is higher than the sum of the cut-in and differential settings, with the system pressure at the desired cut-out point and the contacts closed, turn the grub screw clockwise until the contacts open.

If the cut-in setting is lower than the main scale set-point, with the system pressure at the desired cut-out point and the contacts open, turn the grub-screw counter-clockwise until the contacts close.

Observe the pressuretrol operation over several cycles before replacing the cover.

SteamingatMohawk

Your 50% comment is correct to the extent that the absolute value of the cut-out is dependent on the cut-in. But the differential is independent of the cut-in. I fully understand that concept.

Based on what you said above, if the cut-in is higher than the scale, the screw gets turned clockwise. Based on your experience, can you estimate how many turns might be needed to get it right to eliminate the 0.5 difference between the scale and the actual setting.

Additionally, if/when I try it, the calibration point between the two probably should not be tried at the 0.5 level, but some amount above, so any mismatch with the cut-in spring tension is not a factor in the setting. This may sound complicated, but I believe most guys/gals understand my point.

When you mentioned the tiny screw, I thought it might be the manufacturer's way to accurately set the cut-in calibration. The fabrication of this kind of device is probably not so precise as to make it unnecessary for the actual setting to be able to be adjusted because of manufacturing tolerances, etc.

That being said, I also believe some DIYers may not be knowledgable enough to understand that nuance. However, overall, I have been very favorably impressed with the quality of the comments and help offered in the discussions on this web site. I came across it by chance and have benefited greatly.

I don't live at the house where the system is, so I can't just walk downstairs and look at whatever I want whenever I want.

Thanks for the tutorial. Perhaps, if I can successfully get the 0.5 psig cut-in to be at that point on the scale, I won't bother with a vaporstat and can save myself some money.

Hap_Hazzard

SteamingatMohawk said:

Based on what you said above, if the cut-in is higher than the scale, the screw gets turned clockwise. Based on your experience, can you estimate how many turns might be needed to get it right to eliminate the 0.5 difference between the scale and the actual setting.

No, I'm afraid I can't. You just have to turn until you hear the switch click, and it usually takes a few passes to get it just right. (Of course, a lot depends on how fussy you are.)

SteamingatMohawk said:

When you mentioned the tiny screw, I thought it might be the manufacturer's way to accurately set the cut-in calibration. The fabrication of this kind of device is probably not so precise as to make it unnecessary for the actual setting to be able to be adjusted because of manufacturing tolerances, etc.

Yes, that's exactly what it's for, notwithstanding that they're rarely calibrated accurately out of the box. The presence of the lock-paint is their way of saying it's not supposed to be adjusted by the installer—much less the user—but if they can't do it right, somebody has to, right?

SteamingatMohawk

Agreed, and the paint probably keeps it from working loose and turning.