Designing an upstream wye strainer with a flushing valve

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Old 06-12-14, 04:50 AM
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Designing an upstream wye strainer with a flushing valve

This is for a Burnham V 905 series steam boiler, small commerical, 4GPH. There is a Hoffman Boiler Feed Series VBF Model 30-VBFS-B condensate tank. Feeding it from a 1/2" domestic water supply, there is a Watts 9D-M3 backflow device and then a Bell and Gosset FB-38TU pressure reducing valve.

About every 18 months we've had to replace the FB-38TU pressure reducing valve because it apparently leaks. As a result, the condensate tank slowly feeds water all the time, and subsequently the boiler floods.

The strainer in the FB-38TU cruds up pretty fast, and has been replaced since they disintegrate so easily. At the same time, I've flushed the valve with the strainer removed and it hasn't stopped it from malfunctioning.

I've seen references here to using a wye strainer with a flushing valve to protect devices from crud. Is there anything else I can do to protect these devices from the onslaught of crud from the city water?

If the wye strainer with a flushing valve route is recommended, what brand(s) or specific models would be recommended and/or highly reliable over time?

As a sidenote, the inlet side mesh screen in the 9D-M3 backflow device barely collects a thing, so am in need of something that collects smaller particles.
 
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Old 07-15-14, 05:01 PM
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Found feeder valve totally crudded with hard particulate matter, almost rocklike.

What can I do to insure a clean line going to the boiler from the street?

This is the nipple leading to the Hoffman tank's valve, muck continued into the valve making it useless from crud buildup. Flushing while removed was futile.

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Old 07-15-14, 06:19 PM
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What is the source and quality of your makeup water? Do you have similar problems with other water appliances?

I'm on city water and have a 10-micron whole-house filter on the water coming in from the street. You could install such a filter on the makeup line to your boiler.

Afterthought: could the gunk be coming from the condensate, not the makeup water? If so, filtering the makeup water wouldn't help. Are you periodically blowing down the boiler?
 

Last edited by gilmorrie; 07-15-14 at 07:12 PM.
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Old 07-16-14, 05:04 AM
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City water, it's great. No problems at any fixtures and I clean minimal sediment trapped in the sink aerators every few years. Don't understand why the boiler water line collects crud like no faucet does.

Don't think condensate water would backflow through the valve assembly, could be wrong.

In addition to the black mud and fluid shown, some of the blockage is coal like and can be crunched. What is that stuff?
 
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Old 07-16-14, 05:57 AM
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I wonder what the Manganese content of your water is?

Other possibilities could be Magnetite which is a form of Iron Oxide (I think it has one extra ion or something like that).

Perhaps it's an electrolytic issue... something in the water precipitating out in the presence of electric current... try a dielectric union?

I don't think the strainer screens on wye strainer are any finer than on the 9D so that may not be an option.

I like Gil's idea of a 'Big Blue' 10u filter, but if the contaminant is 'clear water iron' that is forming magnetite the filter won't remove it because it's in solution.

Ask the city for a water report that shows PPMs of all the 'stuff'.
 
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Old 07-21-14, 12:26 PM
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Gotta give in

This is for a Hoffman VBF boiler feed.

I guess I have to drain the tank some so the float drops (to open valve) and flip the fast fill lever on the PRV to flush whatever that is from the lines.

Don't see any other way of assuring a clean line, other than tearing it apart for inspection....

Water quality around here is supposed to be top notch, and aerators at the sinks hardly ever collect any silt. So I'm baffled as to what that stuff is.
 
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Old 07-21-14, 03:25 PM
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Easy enough to try a dielectric union on the water line. That's probably where I would go first.

You'll have to cut the pipe to install the union, so why not throw a filter in there at the same time?
 
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Old 07-22-14, 06:40 AM
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Further

Where in line would you suggest the dielectric, and how would it be beneficial? I thought it was related to galvanized fittings. Here we have cast iron, copper, bronze and brass in close proximity.

Thought of a filter and found some perverse sarcasm in filtering the water to the boiler but not the faucets. Where are my priorities if I do that??

I put the new parts(s) in without issue.

Thanks for your insight.
 
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Old 07-22-14, 03:03 PM
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Anytime there are two dissimilar metals in contact, and in the presence of an electrolyte (the water), a galvanic reaction (think battery) can occur and cause corrosion. The corrosion is caused by movement of ions into and out of the cathode and anode of the 'cell'. In effect, one of the 'electrodes' gives up it's material and deposits it on the other. This is the reason for 'sacrificial anodes' in water heaters and on boats.

The further apart the two metals are on the 'nobility chart', the higher the current and the faster the corrosion. Copper, Brass, Bronze are 'almost' the same metal, and not far apart, thus rarely a problem. Throw cast iron into the mix and there is sometimes a problem.

If the water supply lines are bonded to the building electrical system ground (they should be), there can be external currents (other than the self-generated galvanic reaction) flowing and this can compound the problem.

If you want some more reading, this Wiki article looks good at first glance:

Galvanic corrosion - Wikipedia, the free encyclopedia

perverse sarcasm
Ahhh, now there's something I'm adept at!
 
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Old 07-27-14, 07:52 AM
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Couldn't leave it hanging

Thanks for the insight, excellent explanation.
 
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Old 07-28-14, 04:27 PM
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Thanks O.G. , appreciate the kudos and the 'closure'.

I would be interested if you find the solution!
 
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Old 08-21-14, 07:09 AM
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Maybe

I think it'll be OK if I add flipping the fast fill lever momentarily on the PRV to flush the line with pressure to the routine of flushing the LWCO.

I don't know if that will be detrimental to the float valve.... recall somewhere it said to limit pressure to 30 and am hoping I don't blow it or something like that with a quick surge. Don't know how else to keep the line from accumulating terminal crud. Is there a better way?

The system has been perfect since changing out the parts.
 
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