Entropy

Relax in southern comfort on the east bank of the Mississippi. You're just around the corner from Beale Street and Sun Records. Watch the ducks, throw back a few and tell us what's on your mind.
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JR.
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Re: Entropy

Post by JR. » Thu Apr 22, 2021 12:02 pm

The pump pulled immediately the first time, but then reverted back to reluctant priming the next times. This doesn't make much sense, one obvious difference is first time the outlet discharge pipe was empty so no back pressure.

I am quickly losing interest as replacement pump arrives tomorrow. So will my Y screw drivers so I may unscrew the top of the pump chamber to see if there is anything funny there.

JR

[update- It looks like the RTV o-ring fix worked (for now). My mixed results this morning was because the level threshold on the after market float switch
was set too low... The standing water needs to be up to the pump impeller level or it won't prime. All better now, but not sure I trust this for primary use so tomorrow I will put the new one down into my crawl space. /update]
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terkio
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Re: Entropy

Post by terkio » Fri Apr 23, 2021 5:52 am

It seems this troublesome pump has no foot valve or this valve is bad.
( Forgive me, I do not know wether sump pumps have a foot valve )
With the centrifugal pumps, I know well, a leaky foot valve is about the second trouble next to air leak at the intake side.

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Re: Entropy

Post by JR. » Fri Apr 23, 2021 11:49 am

terkio wrote:
Fri Apr 23, 2021 5:52 am
It seems this troublesome pump has no foot valve or this valve is bad.
Don't know what that is.... OK just looked it up, a check valve on the inlet side of pump.

This is a typical (cheap) submerged pump intended to sit down in a hole (well), so bottom of pump cavity is open to beneath.
( Forgive me, I do not know wether sump pumps have a foot valve )
With the centrifugal pumps, I know well, a leaky foot valve is about the second trouble next to air leak at the intake side.
Arguably my RTV o-ring fix is sealing an intake side possible air leak, but that is underwater in use so shouldn't(?) matter as it would allow more water into pump chamber.
------
As often happens in such matters is am learning more than I want or need to know about pumps.

Apparently another known issue is "air lock" presumably on the output side, if the chamber becomes pressurized with air, it won't pull enough water to engage with impeller.

The new 1/4HP pump has an air vent hole to prevent air lock. In operation water sprays out of that small vent hole.

Of course none of this explains why my current 1/2 horsepower pump seems to lock up (air lock?). When I get my "Y" screwdrivers I can take it the rest of the way apart and look for a blocked air vent hole. The RTV improved seal "seems" to pump reliably as long as pump is started while sitting in water deep enough to engage impeller.

From inspection I see no evidence of (good?) design in the 1/2 HP pump chamber to steer water.. Just an impeller sitting in the middle of the pump chamber. Now after years of the old pump working down in my crawl space I find customer feedback complaining about failures to start pumping from modest depths.

At this point I only have an academic interest in the old pump. My replacement is on a big brown truck in transit to my house.

The new pump is from a 20 YO US company so hopefully they copied a more reliable design. I feel lucky. I am looking forward to putting this back into service and forgetting about it.

JR

[update- No plan survives contact with enemy... the 1/4hp pump arrived and it's 1.25 NPT output port doesn't fit my 1.25" discharge hose. I found an NPT-to barb adapter for $6. As long as I was buying little stuff I purchased a check valve for the output. This will prevent the hose emptying back into the crawl space causing the pump to short cycle. == The 1/4HP flow is noticeably less than the 1/2 HP pump... but not really a problem, it should be able to easily keep up with subsurface ground water flows. /update]
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terkio
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Re: Entropy

Post by terkio » Sat Apr 24, 2021 3:31 am

An air leak at the intake side is no problem if underwater.
Indeed air locks at the output is an issue.
While priming, all air trapped and bubbles must be flushed out. The pump is fully primed only when all air has been purged.
So the out pipes should have the right shape to prevent air traps.
A small vent does help to clear the pump from air.
The pumps I know do not have such a vent, that is not compatible with a pressure tank ( a can that keeps the out piping under pressure and provides some gallons of water while the pump is at rest ).
I learned a lot from a pump to get water from a creek and a pump to provide a house with rain water from tanks.
It took me months to understand it all, it is a slow process, I think we had about it all...
The river pump is more complex using an injector to raise water higher. Very finicky about priming.

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JR.
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Re: Entropy

Post by JR. » Sat Apr 24, 2021 8:56 am

It is raining right now and I am momentarily without a sump pump in place... after it stops raining I will drop the 1/4 HP into the crawlspace with a 3/4" garden hose for output, next week I will scale up to the 1 1/4" hose.

I still haven't taken the old pump top housing apart,,, I do recall air bubbles coming out of it while underwater at one point. Not an obvious vent hole, but perhaps venting to inside the housing then air leaking out of a gap.

I still have no explanation for why improving the o-ring seal with RTV helps the 1/2 HP start.

JR

[update the Y screwdrivers are too small... /update]
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terkio
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Re: Entropy

Post by terkio » Sun Apr 25, 2021 10:08 am

Centrifugal pumps are simple in the principle.... But all is in the details, and there are many variations according to different needs.
Pumping does require the impeller running in water. Air is the enemy.
There are tricks and so callded self priming pumps, but more or less effective, if not plain commercial ballony.

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Re: Entropy

Post by JR. » Sun Apr 25, 2021 12:48 pm

terkio wrote:
Sun Apr 25, 2021 10:08 am
Centrifugal pumps are simple in the principle.... But all is in the details, and there are many variations according to different needs.
Pumping does require the impeller running in water. Air is the enemy.
There are tricks and so callded self priming pumps, but more or less effective, if not plain commercial ballony.
This pump is not described as self-priming more like a submersible, which ASSumes starting while underwater.

From observation nothing about the 1/2 HP design impresses me, including multiple negative customer reviews. Looking at a cutaway image of the 1/4 HP shows a shaped shroud around the impeller steering water toward the output chute, the 1/2 HP design clearly works after water is already moving, but it getting it moving in the right direction seems a little dodgy.

First the good news. I placed the 1/4HP down in my crawlspace with a 3/4" garden hose on the outlet and even with its reduced flow it was able to empty my crawl space in a couple hours. 3" is above average for daily rain fall, so I have no concerns about reduced flow capacity.

The only bed news is that is gets into a short cycle scenario after emptying the crawl space... there is still subsurface water flowing even days after the rain fall, so cycling on and off is normal, but the on time seems to be the 10 second delayed off time. Suggesting that the level threshold may be borderline too low. It is mounted as low as the screw clamp can sit on the pump body. With the threshold higher, the extra ten seconds of pump time after draining down to the threshold will create hysteresis for less short cycling.

Next week I expect the adapter to connect to my 1-1/4" discharge hose, and an inline outlet flow check valve that will prevent discharge hose water draining back into the hole. So until the rest of my parts arrive I will manually cycle the pump on and off. When this is running it is so quiet I can't hear it from inside the house. The old pump was clearly audible.

Good progress and a plan to get this even better (as I learn more).

JR
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terkio
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Re: Entropy

Post by terkio » Mon Apr 26, 2021 10:30 am

Because the access to your crawl space seems troublesome, the alternative to a submerged pump is a surface pump.
In this configuration the pump is at ground level or a bit higher at an easy access location.
Down you only have passive stuff: Intake pipe and foot valve. Here you do need, no air leak for all intake tubing out of water and a foot valve without any leak.
But.....In your application, you need a float switch down there....

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Re: Entropy

Post by JR. » Mon Apr 26, 2021 1:41 pm

terkio wrote:
Mon Apr 26, 2021 10:30 am
Because the access to your crawl space seems troublesome, the alternative to a submerged pump is a surface pump.
In this configuration the pump is at ground level or a bit higher at an easy access location.
Down you only have passive stuff: Intake pipe and foot valve. Here you do need, no air leak for all intake tubing out of water and a foot valve without any leak.
But.....In your application, you need a float switch down there....
My 1/2 HP pump had a tethered float switch that was useless so I tied it up (always on) and added an after market float switch. That aftermarket switch is what got fried by the lightning.

The replacement float switch works and my 1/4 HP pump doesn't have a float switch so simpler to interface.

It is down in my crawlspace now and working but the after market cut off level switch needs to be set a little bit higher to prevent the short cycling, near constant running with cavitation. It says it will pull down to 1/8" but won't start from that low. Right now the low level cut off is about 1" from the bottom of the pump which is best I could do using the stock bracket, but I can put the screw clamp thru holes in the float assembly cage and relocate it higher. The controller has an extra 10 sec on time after reaching the low water threshold... when set properly this extra 10 secs provides some nice hysteresis. Right now it comes on too frequently and only for the extra 10 seconds, the threshold needs to be high enough to pull solid water before the extra 10 seconds run time.

My check valve and adapter to fit my 1-1/4" discharge hose is scheduled to arrive Wednesday. Until than I can switch it on/off manually. Since it hasn't rained for days, it only runs for a few minutes at a time, before pulling air.

I remain optimistic I am close to end of this journey.

==

In hindsight since the RTV o-ring fix I could probably keep using the 1/2HP but I feel better about the 1/4HP being a better fit for my application. It already pumps out the water fast enough, but with the 1-1/4 discharge hose it will move even more water. The check valve will prevent any chance of back flow from the discharge hose. I have seen that before.

JR
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Re: Entropy

Post by JR. » Thu Apr 29, 2021 10:02 pm

Now I am anxiously waiting for the next rain storm so I can learn if my improved sump pump system works better.

I am optimistic the check valve will prevent short cycling. The bad news is the added plumbing attached to the top of the pump discharge outlet has made it top heavy and less stable standing straight up. But I remain optimistic.

I purchased a stainless steel strainer to use as a basket to sit it in and keep major debris from clogging it up.

Today I moved some loose bricks into the bottom of the well hole so it isn't sitting on and sucking up loose sand.

The bricks and basket have added some height so I will have to wait until it rains to see if it is adjusted low enough.

I feel lucky that even if it tips over it will still function.

I shouldn't have to wait too long for rain... I live in MS. Showers or thunderstorms forecast next several days.

JR
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