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Re: [hobbicast] Re: My New Aluminum Tilting Furnace

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  • Jamie Cunningham
    That s the easiest idea yet! I could probably find a valve that fits the pipe I m already using :) although things ARE working now - that s a good idea if I
    Message 1 of 43 , May 5, 2011
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      That's the easiest idea yet! I could probably find a valve that fits the
      pipe I'm already using :)

      although things ARE working now - that's a good idea if I wanted to NOT go
      full blast sometime

      Thanks!

      On Thu, May 5, 2011 at 9:32 AM, frozen chosen <walter2@...>wrote:

      >
      >
      > On my son,s forge we have a shop vac running off exhaust port and we
      > control the air pressure with a T fitting and two ball valves. We hooked
      > the supply to one side of the top leg and run it straight into a ball
      > valve to the forge , the bottom leg has a ball valve to the out side
      > air. By adjusting the two valves we can get the pressure we need from
      > max air to 0 air. Also the T fitting and the ball valves are 1 inch pvc
      > to iron black pipe but with the air flow and the length of 1 inch iron
      > pipe ,the pvc doesn't get warm.
      >
      >
      >


      [Non-text portions of this message have been removed]
    • Evan Daniel
      The 746 W/HP conversion is quite relevant: Input watts * efficiency = output watts; output watts / 746 = output HP. All motors have less than unity efficiency,
      Message 43 of 43 , Jul 11, 2011
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        The 746 W/HP conversion is quite relevant: Input watts * efficiency =
        output watts; output watts / 746 = output HP. All motors have less
        than unity efficiency, so output watts *must* be less than input
        watts. So a 3HP motor that runs on 120V, 15A service is obviously
        lying about the output power. (Input power of at most 1800W, output
        power of 2240W is not physically possible.) In general, an assumption
        that electric motors run between 80% and 95% efficiency will serve
        well. Less for very small motors, and the high end of that only on
        large, expensive, high-efficiency motors.

        Note also that input watts is *not* simply input volts * input amps on
        an AC circuit. Input watts = Input volts * Input amps * power factor.
        Power factor is always <= 1, and is 1 only for a purely resistive
        load. Inductive loads like motors will present a power factor of less
        than 1. So a 10A, 120V input motor might only draw 900W of input
        power, and then output 1HP of shaft power.

        Evan Daniel

        On Mon, Jul 11, 2011 at 10:19 AM, Howard Wilkinson <owly@...> wrote:
        >    The 746 figure is a physical equivalency between horsepower and
        > wattage, and has no relationship whatsoever with real world shaft
        > horsepower in relation to input wattage.   In honest real world
        > "industrial duty" a 5 Hp single phase motor running on 240 vac will draw
        > anywhere from 25 to 30 amps at full load.... that's about double the
        > theoretical relationship.   The difference between the two motors (25
        > and 30 amp), is not efficiency, but reliable continuous output.  The 30
        > amp unit will run virtually forever at full load, dissipate the heat
        > generated easily, etc... the smaller one less so, but still good.    You
        > will however find motors labeled "compressor duty", rated at 5 HP that
        > are rated for around 15-16 amps.   These obviously carry a horsepower
        > rating that is purely theoretical, and based on the 749 figure.  They
        > are in no way equivalent, and will not even begin to do the job of the
        > other larger motors.
        >    My personal rule when looking at motors is to look at current
        > draw.....using 5-6 amps per  horsepower on 240 VAC per horsepower or
        > 10-12 amps per hp on 120 VAC.  They lie and exaggerate so much that this
        > is the only way to get a real idea of what you are looking at.
        >    Interestingly, they tend to represent these differences as
        > efficiency, when in fact they are not.... the lower rated motors are NOT
        > more efficient, they simply do less work.  One encounters the same kinds
        > of deception with gasoline engines.  There is a simple cubic feet per
        > minute (air flow) formula that quickly reveals the truth in that
        > instance.   The amount of airflow per HP is very consistent, and much
        > more reliable than the smoke and mirrors generated by clever dyno
        > operators.   It is after all the work a motor or an engine does that
        > matters, NOT the numbers.    For most folks it doesn't matter...  they
        > proudly haul  home their "5 Hp" compressor...it makes noise, and pumps
        > air, and they have no real need of the kind of output a real 5 HP
        > produces anyway, so they are satisfied and the company sells their
        > product.... no harm done!
        >
        >
        >
        >    Howard
        > On 07/11/2011 07:21 AM, Evan Daniel wrote:
        >> Shop vac horsepower ratings have little, if anything, to do with the
        >> usual definition of 1 HP = 746 watts. Note that the maximum real HP of
        >> a motor plugged into 120V 15A service is 2.4 HP theoretical; in
        >> practice, you can't get perfect power factor or perfect efficiency,
        >> and the largest motor you'll see is about 1.5 HP. At work we have a
        >> 6.5 HP shop vac that runs on 120 V, 15A service.
        >>
        >> (Also, shop vac motors will be somewhat smaller than you'd expect
        >> because they run at high speed. High-rpm motors are generally more
        >> compact.)
        >>
        >> Also, returning to topic... I use a shop vac and butterfly valve for
        >> my aluminum casting furnace; works great.
        >>
        >> Evan Daniel
        >>
        >> On Sun, Jul 10, 2011 at 9:25 PM, Alan <rustaholic777@...> wrote:
        >>
        >>> I tore a sears shop vac apart to remove the motor and use it for a tank to catch sawdust by using a newer shop vac to pull air through the old one.
        >>> We have two of these setups at work.
        >>> I was surprised to see what a puny motor was in there since the vac was rated at 3 1/2 HP.
        >>>
        >>> Alan
        >>>
        >>> --- On Fri, 5/6/11, Stone Tool <owly@...> wrote:
        >>>
        >>>
        >>> From: Stone Tool <owly@...>
        >>> Subject: Re: [hobbicast] Re: My New Aluminum Tilting Furnace
        >>> To: hobbicast@yahoogroups.com
        >>> Date: Friday, May 6, 2011, 10:37 PM
        >>>
        >>>
        >>> You guys are drawing the wrong conclusion here.   a vacuum cleaner is a
        >>> centrifugal blower, not a positive displacement blower.   Blocking
        >>> either the suction or the exhaust REDUCES MOTOR LOAD..... You will
        >>> notice that the RPM goes UP, not down when you block either inlet or
        >>> outlet.    I've owned quite a few shop vacs over the years, and all of
        >>> them have had cooling fans on the motor.    These are brush motors, and
        >>> unlike induction motors, the speed varies with the load... load them
        >>> down, they lose RPM, unload them and they rev up.    You can tell the
        >>> truth of what I am saying by simply listening to your vac.   Using the
        >>> selector Tee will make it work harder, not less..... There seems to be a
        >>> major misunderstanding of the operation of these machines going on
        >>> here.    If you can lay hands on a clamp on amp meter,  you can see for
        >>> yourself.        Being brush motors, they probably can be controlled
        >>> using a rheostat, like an electric drill or a sewing machine motor.   I
        >>> would suggest finding an old sewing machine foot pedal and
        >>> experimenting.  It could be adapted to control the RPM and airflow on
        >>> the shop vac.  These usually are cheap motors, not designed for long
        >>> life.... brush motors seldom have a long life.... brushes wear out, and
        >>> often take the commentator, just like a cheap hand drill or 4" grinder.
        >>>
        >>>
        >>>                                                 Howard
        >>>
        >>> On 05/06/2011 11:06 AM, oldstudentmsgt wrote:
        >>>
        >>>> All things considered, the T valve setup is better, as it lets the vacuum motor run full speed with no restrictions on the airflow through the motor. Anything that blocks the airflow, as opposed to diverting part of it, will cause the vacuum motor to overheat if it's one of those that uses it's own airstream for cooling. (AFAIK, that is most of them.)
        >>>>
        >>>> HTH
        >>>>
        >>>> Bill in OKC
        >>>>
        >>>> --- In hobbicast@yahoogroups.com, frozen chosen <walter2@...> wrote:
        >>>>
        >>>>
        >>>>>   On my son,s forge  we have a shop vac running off exhaust port and we
        >>>>> control the air pressure with a T fitting and two ball valves. We hooked
        >>>>> the supply to one side of the top leg and run it straight into a ball
        >>>>> valve to the forge , the bottom leg has a ball valve to the out side
        >>>>> air. By adjusting the two valves we can get the pressure we need from
        >>>>> max air to 0 air. Also the T fitting and the ball valves are 1 inch pvc
        >>>>> to iron black pipe but with the air flow and the length of 1 inch iron
        >>>>> pipe ,the pvc doesn't get warm.
        >>>>>
        >>>>>
        >>>>>
        >>>>
        >>>>
        >>>> ------------------------------------
        >>>>
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        >>>>
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        >>>>
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        >>>>
        >>>
        >>>
        >>> ------------------------------------
        >>>
        >>> For discussion of Metal Casting and related issues
        >>> this list does not accept attachments.
        >>>
        >>> Files area and list services are at:
        >>>      http://groups.yahoo.com/group/hobbicast
        >>>
        >>> For additional files and photos and off topic discussions
        >>> check out these two affiliated sites:
        >>>      http://groups.yahoo.com/group/sandcrabs
        >>>      http://groups.yahoo.com/group/Hobbicast1
        >>>
        >>> Please visit our sponsor: Budget Casting Supply
        >>> http://budgetcastingsupply.com/
        >>>
        >>> List Owner:
        >>> owly@...
        >>>
        >>> Yahoo! Groups Links
        >>>
        >>>
        >>>
        >>>
        >>>
        >>> [Non-text portions of this message have been removed]
        >>>
        >>>
        >>>
        >>> ------------------------------------
        >>>
        >>> For discussion of Metal Casting and related issues
        >>> this list does not accept attachments.
        >>>
        >>> Files area and list services are at:
        >>>     http://groups.yahoo.com/group/hobbicast
        >>>
        >>> For additional files and photos and off topic discussions
        >>> check out these two affiliated sites:
        >>>     http://groups.yahoo.com/group/sandcrabs
        >>>     http://groups.yahoo.com/group/Hobbicast1
        >>>
        >>> Please visit our sponsor: Budget Casting Supply
        >>> http://budgetcastingsupply.com/
        >>>
        >>> List Owner:
        >>> owly@...
        >>>
        >>> Yahoo! Groups Links
        >>>
        >>>
        >>>
        >>>
        >>>
        >>
        >> ------------------------------------
        >>
        >> For discussion of Metal Casting and related issues
        >> this list does not accept attachments.
        >>
        >> Files area and list services are at:
        >>      http://groups.yahoo.com/group/hobbicast
        >>
        >> For additional files and photos and off topic discussions
        >> check out these two affiliated sites:
        >>      http://groups.yahoo.com/group/sandcrabs
        >>      http://groups.yahoo.com/group/Hobbicast1
        >>
        >> Please visit our sponsor: Budget Casting Supply
        >> http://budgetcastingsupply.com/
        >>
        >> List Owner:
        >> owly@...
        >>
        >> Yahoo! Groups Links
        >>
        >>
        >>
        >>
        >>
        >
        >
        >
        > ------------------------------------
        >
        > For discussion of Metal Casting and related issues
        > this list does not accept attachments.
        >
        > Files area and list services are at:
        >     http://groups.yahoo.com/group/hobbicast
        >
        > For additional files and photos and off topic discussions
        > check out these two affiliated sites:
        >     http://groups.yahoo.com/group/sandcrabs
        >     http://groups.yahoo.com/group/Hobbicast1
        >
        > Please visit our sponsor: Budget Casting Supply
        > http://budgetcastingsupply.com/
        >
        > List Owner:
        > owly@...
        >
        > Yahoo! Groups Links
        >
        >
        >
        >
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