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Author Topic: Stump the engineer...  (Read 3581 times)
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« Reply #15 on: May 10, 2010, 11:56:16 PM »

I bet you that it's a soft metal> maybe brass..

Have you ever drained your system.

If you had a hose attached to you water system and stretched out downhill you "could" pull enough vaccuum to see what you have recorded with the bent needle.
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« Reply #16 on: May 11, 2010, 01:15:10 AM »

How about a pressure spike slamming the needle full around against the stop bending it.  06 Bill
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« Reply #17 on: May 11, 2010, 05:26:38 AM »

As a instrument tech in a previous life, this looks like a water hammer to me.......!   When stopping a pump this happens, also can happen when valves close quickly.  Putting a dampner pressure gauge would help prevent this if the gauge is that important but probably not worth the price in this use!  When slamming to zero the pointer beats itself against the stop.......bending the pointer.
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« Reply #18 on: May 11, 2010, 06:20:57 AM »

Sean,

I thought you had a small pressure tank in your fresh water system? I would think that would prevent an excessive drop in pressure on the line when the toilet is flushed, but
maybe not if the line is small and the gauge is on the output side of the regulator (which it certainly must be).

I use a similar regulator on my fresh water, but only on the incoming shore line. It protects the entire system from high municipal pressure. My pump regulates to 60 lbs internally, and
I use a couple 2 gallon pressure tanks to even everything out. I'll check my gauge, but I'm pretty sure it has not experienced what you are seeing on yours.

I do believe yours is related to the small line it's on and the very low volume between the regulator and toilet. I don't fully understand why you have it on there? Does your toilet require
something less than 60 lbs? 

BTW, they make a pressure regulator for garden use that regulates to 35 psi with no gauges or adjustments. It simply screws onto a standard hose bib fitting. I believe I have one here.
If you are interested in using something like that, I'll dig it out and send it to you.

craig
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Craig Shepard
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« Reply #19 on: May 11, 2010, 07:36:29 AM »

Small amount of force, but multitude cycle of repeated impact to the stop may have caused the indicator to bend.
The indicator may be made of ductile aluminum.

AJ
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RichardEntrekin
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« Reply #20 on: May 11, 2010, 09:52:30 AM »

Bourdon tube pressure gauges do not tolerate chronic big pressure swings over and over again without going out of calibration. I know this from experience with using the same gauge on bicycle pumps. They don't last long. If the gauge went out of cal, it would allow it to hammer against the stop with each flush. It would be curious if you knew where you set the pressure on the regulator initially, and where the pressure reads when you install a new gauge.

Just a theory.
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« Reply #21 on: May 11, 2010, 10:08:27 AM »

...
Ever freeze that water line? (cold weather)
Ever had a vapor-lock condition in that line? (hot weather)
...


No, the gauge, regulator, and all the plumbing to it has been environmentally controlled since day one.  So no freezing or boiling.  We have pets, so we need to keep the coach within reasonable living temperatures even when we are away from it.

But:

Quote
Ever run out of flush water?


Yes.  We normally keep the pumps on 100% of the time, but on occasion we have turned them off for whatever reason, usually because one of the hot water recirculating valves is leaking and we are trying to preserve the hot water.  Once in a while we forget the pump is off, and try to flush the toilet anyway.  This always has bad consequences, since the cycle valve in the Microphor depends on having both air and water pressure to it at all times.  I'm certain this causes the pressure to drop to zero, but since this gauge is on the output side of the regulator, that should be a gradual drop-off.

...
Have you ever drained your system.

If you had a hose attached to you water system and stretched out downhill you "could" pull enough vaccuum to see what you have recorded with the bent needle.


We've never drained the pressure side of the system.  There is a check valve on the city water inlet, so even with a hose attached, there's no way for the pressure to drain out that way.  We never use city water pressure, as a rule, either.  I think we've been hooked to city water maybe three times in six years, and in all cases it was either for testing or to do maintenance on the pump.  Generally, even when city water is available, we just fill our tank and use our internal pump for pressure.

How about a pressure spike slamming the needle full around against the stop bending it.


As has already been mentioned, that would have bent the needle the other way.  The bend in this direction can only be cause by hitting the zero stop on the downward swing.

As a instrument tech in a previous life, this looks like a water hammer to me.......!   When stopping a pump this happens, also can happen when valves close quickly.


OK, we've had some hammer.  Generally this happens when we run out of fresh water in the tank, and the pump ingests some air into the lines.  We'll get hammer until we purge all that air out.  I can't say that I've watched this gauge when this happens, but next time I will.

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Putting a dampner pressure gauge would help prevent this if the gauge is that important but probably not worth the price in this use!


That is surely true.  Same for the earlier recommendation to change to oil-filled.  I want to figure out what caused this, but it's not worth it to me to fix the gauge itself.  It's only purpose was to adjust the water pressure initially, and it's not mounted anyplace where it can even be seen in normal use.

...
I thought you had a small pressure tank in your fresh water system?


No, we have Sensor VSD pumps, which do not require an accumulator tank.

Quote
I would think that would prevent an excessive drop in pressure on the line when the toilet is flushed, but
maybe not if the line is small and the gauge is on the output side of the regulator (which it certainly must be).


The supply line to the regulator is 1/2' ID, as are all our water lines (PEX).  From the regulator to the fixture is one of those braided stainless connector hoses from the hardware store.  That said, I would guess the orifice in the regulator to be much smaller, say 1/8" or less.

Quote
..
I do believe yours is related to the small line it's on and the very low volume between the regulator and toilet. I don't fully understand why you have it on there? Does your toilet require
something less than 60 lbs?


Yes.  The way this contraption works, the cycle valve controls the timing and operation of the flapper door, the blast of compressed air that shoots the waste to the tank, and the refill of the bowl.  The cycle valve has no adjustments on it.  Timing and operation are controlled completely by pressure and flow rates in the air and water supply.  Microphor requires a dedicated regulator on the air supply, set to 60psi, and we have always had that.  They also strongly recommend a dedicated regulator on the water supply, too.  We tried to live without one, since we always run just on pump pressure and that's a pretty constant pressure.

The problem with that was that our pump pressure delivered water to the system at a rate that cause the bowl to fill too far.  We tried for a long time to control this with a gate valve at the fixture, adjusting the orifice down to a point where the flow was lower.  But that was unreliable, and especially when there was any variation at all in delivery pressure, such as when connected to city water (rarely), or after a change in battery voltage such as turning the charger on, which creates a temporary pressure surge the next time you turn the water on.

Ultimately, we gave up and sprung the money for a small individual regulator at the fixture.  Then we dialed the pressure at the fixture down until we got the minimum amount of water in the bowl.  The spec calls for two quarts per flush, and before we installed the regulator, we were using much more than that -- I would say closer to two and a half quarts.  When you spend two weeks at a time in the desert, that extra pint every flush takes a toll both on the fresh water supply and the black tank capacity.

I remember the regulator as being quite spendy, like around $40.  It was available with or without a gauge, and the gauge was only a couple bucks extra, so we got it, even though we really use the amount of water delivered to the fixture as the yardstick for adjustment, rather than the pressure reading.

As you can see in the photo, we have the pressure dialed down considerably.  So you can imagine how much extra water we'd get at a much higher pressure.

Quote
BTW, they make a pressure regulator for garden use that regulates to 35 psi with no gauges or adjustments. It simply screws onto a standard hose bib fitting. I believe I have one here.
If you are interested in using something like that, I'll dig it out and send it to you.


Thanks, we've got a couple.  We use them in those rare cases where we need to connect to city water to bypass the pump for maintenance.  While our entire water system is rated for pressures far in excess of that, our own skin is now calibrated for the pressure delivered by our on-board pump, and we find ourselves having to fiddle too much with faucets and shower valves if we have significantly higher pressure than that at the taps.

The garden-hose style regulators made for RV use do not have the fine adjustment required for the Microphor application.

The good news is that installing the regulator was the right solution, and everything has worked perfectly since then.  I would not even have noticed the bent pointer if we did not pull the toilet out for other reasons.  It's not so much a problem as a curiosity at the moment.  I've never seen this behavior, and I want to understand it, so the next guy with a Microphor who asks me for advice can benefit from that.

Bourdon tube pressure gauges do not tolerate chronic big pressure swings over and over again without going out of calibration. ... They don't last long. If the gauge went out of cal, it would allow it to hammer against the stop with each flush. It would be curious if you knew where you set the pressure on the regulator initially, and where the pressure reads when you install a new gauge.


Aha!  This is the best answer I have heard yet.  Now that you ask: No, I don't remember what I had the pressure set to.  As I wrote above, we set it by delivery volume, not pressure.  But my fuzzy memory suggests perhaps somewhere around 30 psi, and the photo clearly shows the straight portion of the needle aiming somewhere closer to 20 psi.

I'm not sure it's worthwhile to replace this gauge.  But if I come across a reasonably priced replacement in my travels, I'll do it just to answer this question.

-Sean
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« Reply #22 on: May 11, 2010, 05:17:44 PM »

with steam we put a pigtail in system to help stop guage hammer and other problems.fwiw
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« Reply #23 on: May 11, 2010, 06:28:15 PM »

... we put a pigtail in system to help stop guage hammer and other problems.


I'm sorry, I've never heard this term used in reference to plumbing systems.  Could you please explain it?

Is this a length of pipe or tubing used, essentially, as an accumulator?

Speaking of which, if an accumulator in the toilet service line would help, should it be installed before or after the regulator?

-Sean
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« Reply #24 on: May 11, 2010, 07:13:04 PM »



Speaking of which, if an accumulator in the toilet service line would help, should it be installed before or after the regulator?



After. 

The accumulator provides volume to maintain pressure over longer periods. 

I believe the problem you are experiencing is that the small volume of water on the low pressure side of the regulator is depleted instantaneously when the toilet is flushed
which allows the pressure to drop to 0 very rapidly when the large valve in the toilet is opened. It's an instantaneous drop in pressure because essentially all the volume is
allowed to escape immediately, and the regulator cannot supply enough volume fast enough to replace it.

Of course what this means is that if you put on an accumulator, you will have to recalibrate the volume of water that flows into the toilet, probably by reducing the pressure even more.

If I understand the way your particular model works, it only relies on air pressure to do the actual flushing and then the water valve is opened to replenish the bowl after the flapper is
closed?  Is that correct?

You know, you might want to look into a variable timed relay that controls a solenoid valve. That way you can adjust how long it's open and how much water is allowed through. This
might eliminate the need for an accumulator as you could reduce the size of the opening into the valve using a bleed, and compensate by increasing the time the valve is open.

My Microphor has a time adjustment on the water valve to regulate the amount of water that is used for each flush. Of course the volume varies with pressure, but we only care when we're
boondocking, which is most of the time, so we seldom adjust it.

craig
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« Reply #25 on: May 11, 2010, 07:40:10 PM »

A pigtail is basically a small expansion device (accumulator) and should be placed after the pressure regulator!  Sean they make a snubber that screws into the line, then you turn the gauge into the snubber protecting the gauge.   I don't think you have a enough pressure to actually damage any components other than the gauge! Here is a link that might help!   

http://www.coleparmer.com/catalog/product_index.asp?cls=4231
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« Reply #26 on: May 11, 2010, 08:51:57 PM »

After.  ...


That's what I would have thought...

Quote
If I understand the way your particular model works, it only relies on air pressure to do the actual flushing and then the water valve is opened to replenish the bowl after the flapper is
closed?  Is that correct?


The cycle valve is a one-piece, non-adjustable, complicated contraption.  The flush lever actually activates the air side of the valve.  From there air pressure (1) opens the flapper door to allow all the waste, including the half gallon of water that started out in the bowl, to drop into the "hopper," (2) closes the same flapper door, which is held tightly sealed to a gasket by ~60psi of air pressure, then (3) blasts two gallons (at atmospheric pressure) of air into the hopper to send the waste to the tank through a 1.5" waste line.  At that point, water pressure takes over, operating the last half of the cycle, wherein all the air valves are reset to their pre-operating positions, and the bowl is refilled with half a gallon of water.

If there is no water pressure, the cycle stops in the middle of the air-operated portion, with the flapper door still open.

Quote
You know, you might want to look into a variable timed relay that controls a solenoid valve. That way you can adjust how long it's open and how much water is allowed through. This
might eliminate the need for an accumulator as you could reduce the size of the opening into the valve using a bleed, and compensate by increasing the time the valve is open.


Disabling or disconnecting that portion of the cycle valve in order to do the timing electrically would involve completely re-engineering the cycle valve.  Not something I want to get into.

Quote
My Microphor has a time adjustment on the water valve to regulate the amount of water that is used for each flush. Of course the volume varies with pressure, but we only care when we're
boondocking, which is most of the time, so we seldom adjust it.


Yeah, the air-flush models are completely different from the direct-drop models, whether mechanical or electrical.  Ours operates by air and water alone, no electricity.

A pigtail is basically a small expansion device (accumulator) ...


That's what it sounded like.  But I had never heard the term used that way before.

Quote
Sean they make a snubber that screws into the line, then you turn the gauge into the snubber protecting the gauge.   I don't think you have a enough pressure to actually damage any components other than the gauge!


I think you are 100% correct, and I'm not sure it's even worth the ~$15 for a snubber.  But I might whip together a small accumulator out of some spare PVC plumbing parts just to see if it helps any.  Not on my short-term list, though -- that's a "round tuit" project.

-Sean
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« Reply #27 on: May 12, 2010, 12:09:10 PM »

As you can see, the indicator pointer is bent.  It most assuredly was not when I installed it a couple years ago.

I am mystified.  It looks like the end of the pointer bent on the zero stop.  The only way I can think such a thing could happen is if the water line drew a vacuum, and I would imagine it would have to be a pretty strong one to bend it like that. 

Put a vacuum on the gauge and see how much you need to bring the needle back to the stop.  Then pressurize to working pressure and dump it -- does the needle hit the pin?  It has to be one or the other, OR, it's a plastic needle, spring-loaded to zero tension where the needle now hits the pin, and you had enough heat there (hot water line?  Sunlight?  Electrical?  Ambient temp?) to allow the needle to soften enough to deform.

Whatever the story is, I would definitely want to know before reinstalling, if you are pulling your air from the main system, or if you have a wooden floor or other stuff that will burn.
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« Reply #28 on: May 12, 2010, 12:12:53 PM »

... we put a pigtail in system to help stop guage hammer and other problems.

I'm sorry, I've never heard this term used in reference to plumbing systems.  Could you please explain it?

Is this a length of pipe or tubing used, essentially, as an accumulator?

It's a little stub 6 - 8 inches) attached to the system, capped at the top so it's filled with air and connected back near the faucets.  Go check Home Despot or Lowelife, look where they have the oddball plumbing stuff (like pressure-test gauges).
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« Reply #29 on: May 13, 2010, 08:59:30 AM »

Ok first of all a pigtail is a piece of pipe between the line and the gauge. It literally curls around in a circle. On a steam line, water condenses in the bottom of the circle and thus provides some isolation of the gauge from transient spikes in the line pressure.

A snubber is a simple orifice put between the line and the gauge. One could be made with PVC fittings and a 1/32 drill if you didn't want to put any money in it. Otherwise find one to fit your situation in the McMaster Carr catalog. The small hole eventually allows the pressure to equalize on both sides of the gauge, but dampens transient pressure changes in the line. They work better with liquids than with gases (air)

An accumulator is way overkill to cure the gauge issue. If the toilet is functioning with adequate air flow an accumulator is not needed.

My solution.......put a pipe plug in the hole where the gauge was. You said you set the pressure based on toilet fill. You don't really care what the pressure is.
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