electricpete
Electrical
- May 4, 2001
- 16,774
This is the same pump described in my previous thread thread407-494946
1/2 HP, 115 Volt, 60 Hz, 3.87″ Impeller, 2″ NPT Discharge, 20′ Cord, 3/4″ Solids.
(No, we haven't changed anything since last thread)
We "backflush" or "backwash" this pump with pressurized water source applied to the pump discharge once a week in an attempt to clear out debris which we perceive (rightly or wrongly) is causing the chronic reliability problems. Throttling of the water source is manual. Duration is not specified.
Today another one of these pumps was removed today due to reported starting problems.
We examined it on the bench.
There is no foreign material present in the impeller (just like last time).
There are conflicting reports on whether the pump rotated freely at this point in time.
We energized the motor with 115vac and it just hummed.
Starting capacitor tested expected capacitance (that test was done later but it seems more relevant to present here).
Then we removed the lower cap/flange and retried start and this time it successully it started (we immediately stopped it).
We noted indication of rub between the impeller and the lower cap and also a chip on the "trailing edge" of the impeller (slides 1 and 2).
Bearings seem to be in pretty good shape.
We noted that the vendor literature (slide 2) says "“Backflow can allow the pump to turbine backwards and may cause premature seal and/or bearing wear”. I'm not sure exactly why that is, the best I can figure is the speed is unpredictable during backwash so it may be more likely that you spin the pump at a resonant speed for awhile which might cause damage.
That last one sure had some damaged bearings (looks more like bad quality but maybe backwash contributed who knows). This one had no damaged bearings but there was that chip on the impeller that we're wondering about.
It was theorized that
[ul]
[li]1. perhaps the chip at that particular location (trailing edge of the impeller) was more likely to occur when the pump is rotating backwards.[/li]
[li]2. backwards rotation apparently happens during backwash as stated by the vendor.[/li]
[/ul]
Questions
[ol 1]
[li]Do you believe claim 1?[/li]
[li]Do you believe claim 2? It's hard for me to visualize looking at this impeller. Looking from the bottom at the open face, it normally rotates CW but it would rotate CCW if we put high pressure water into the [normal] discharge port and allowed that water to flow through the pump into the sump?[/li]
[li]Is it your experience that backwashing a pump can cause damage? Is the explanation similar to what I said above (spinning at resonance) or something else?[/li]
[/ol]
Link
=====================================
(2B)+(2B)' ?
1/2 HP, 115 Volt, 60 Hz, 3.87″ Impeller, 2″ NPT Discharge, 20′ Cord, 3/4″ Solids.
(No, we haven't changed anything since last thread)
We "backflush" or "backwash" this pump with pressurized water source applied to the pump discharge once a week in an attempt to clear out debris which we perceive (rightly or wrongly) is causing the chronic reliability problems. Throttling of the water source is manual. Duration is not specified.
Today another one of these pumps was removed today due to reported starting problems.
We examined it on the bench.
There is no foreign material present in the impeller (just like last time).
There are conflicting reports on whether the pump rotated freely at this point in time.
We energized the motor with 115vac and it just hummed.
Starting capacitor tested expected capacitance (that test was done later but it seems more relevant to present here).
Then we removed the lower cap/flange and retried start and this time it successully it started (we immediately stopped it).
We noted indication of rub between the impeller and the lower cap and also a chip on the "trailing edge" of the impeller (slides 1 and 2).
Bearings seem to be in pretty good shape.
We noted that the vendor literature (slide 2) says "“Backflow can allow the pump to turbine backwards and may cause premature seal and/or bearing wear”. I'm not sure exactly why that is, the best I can figure is the speed is unpredictable during backwash so it may be more likely that you spin the pump at a resonant speed for awhile which might cause damage.
That last one sure had some damaged bearings (looks more like bad quality but maybe backwash contributed who knows). This one had no damaged bearings but there was that chip on the impeller that we're wondering about.
It was theorized that
[ul]
[li]1. perhaps the chip at that particular location (trailing edge of the impeller) was more likely to occur when the pump is rotating backwards.[/li]
[li]2. backwards rotation apparently happens during backwash as stated by the vendor.[/li]
[/ul]
Questions
[ol 1]
[li]Do you believe claim 1?[/li]
[li]Do you believe claim 2? It's hard for me to visualize looking at this impeller. Looking from the bottom at the open face, it normally rotates CW but it would rotate CCW if we put high pressure water into the [normal] discharge port and allowed that water to flow through the pump into the sump?[/li]
[li]Is it your experience that backwashing a pump can cause damage? Is the explanation similar to what I said above (spinning at resonance) or something else?[/li]
[/ol]
Link
=====================================
(2B)+(2B)' ?