>The problem is now I have more questions. I have assumed
>that Wes has the info cited above. Thats why I got the pump from
Cinnabar.
>There are many gurus who say the paddle pump is not the right one.
The
>only one we want is the solid disc pump. Do you have any thoughts
that
>you would be willing to share with us on this subject. Anything
form
>horsepower to flow rate would be accepted. I only know what I think
I know
>not what the numbers say. We need you engineer types to read those
>tea leaves for us.
Arch
First I better give you the definition of an "ENGINEER"
An engineer is one who passes as an exacting expert on the strength of being
able to turn out with prolific fortitude, strings of incomprehensible
formula, calculated with microscopic precision from extremely vague
assumptions which are based on debatable incomplete experimentation carried
out with instruments of problematic accuracy by persons of doubtful
reliability and rather dubious mentality, with the particular anticipation
of disconcerting and annoying everyone outside their own fraternity.
With that disclaimer out in the open, I will attempt to help a little more.
A pump with a solid disc (called a "closed impeller") is typically more
efficient than a paddle impeller (called and "open impeller"). The reason
is that there is less slippage of the fluid around the vanes....everything
else being equal...such as clearances, diameter, number of vanes, etc.
So, if all other factors were equal, and one pump had a disc/closed impeller
and another had a paddle/open impeller.....the disc/closed impeller pump
would be more efficient. That means that the horsepower required per gallon
pumped would be less. Efficiency in the GMC application is really not that
important. I think the goal is the "correct" flow for an RPM band. This
could be achieved by pumps of various efficiencies. A low efficiency pump
may not need a flow restrictor, and will use more HP than a higher
efficiency pump. A disc/closed impeller probably flows water better than an
open/paddle impeller at low RPMs (like idle). At cruising RPMs, the flow
difference may be imperceptible. The larger the impeller the greater the
flow for a given RPM (again with all other factors equal). The number of
blades/vanes for a given diameter will probably affect efficiency more than
flow. The "ideal" water pump for the desired service conditions would
probably be a closes impeller with running clearance of about 0.010" and
have precisely contoured and machined vanes in the impellers and flow
straighteners in the volute (casing). However, this would make it a $1,000
- - $ 5,000 pump.
Conclusion: whatever pump configuration(s) that provides the "correct" flow
at the desired RPM band without cavitation are good.
I met the owner of FLOWKOOLER automotive water pumps a few years ago. They
manufacture high performance water pumps. I think that they do this by
upgrading standard pumps. I purchased one for my Ford pick-up a few years
ago. Being an engineer type, I had to take it apart to "inspect" it before
installing. This particular one was "upgraded" by adding a sheet metal disc
to a paddle type impeller. Their general pump flow curve indicated 100%
more flow at 900 RPM, and 20% more at 2000 RPM. So,
if keeping temperature down while setting/idling is an issue, the closed
impeller is probably better. At cruising RPM either is probably OK. I will
try to pick the brain of the owner of FLOWKOOLER in the future....he invited
me for a tour of his facility.
- -Larry (aka engineer type)
73 Painted Desert
>This jibes more or less with what I had
>always heard and surmised. Still wish I understood exactly what
happens to
>the water molecules during shutoff that lowers the power absorbed,
but I
>accept that it happens. Oh well, my 19 yr. old stepdaughter is an
>engineering student at CU, maybe she can explain it in a semester
or two. ;-)
>Rick Staples
Hey Rick....you gave me a pretty easy one here.
The HP going into the pump (energy) is converted to heat energy and raises
the temperature of the water. It friction heats the water by "beating" it
with the impeller vanes instead of pumping it. So, the water molecules just
absorb the energy as heat rather than as mass flow energy. Most centrifugal
pumps that have a valve to shut off the discharge have a minimum flow bypass
line to provide the minimum acceptable flow to prevent overheating. Large
industrial centrifugal pumps are started at shutoff (if possible) to
minimize starting HP. A good example of friction heating of fluid by a pump
is a nuclear power reactor. Upon start-up, water in the system is heated by
running the reactor recirculation pumps (huge vertical "GMC water pumps") in
a closed loop mode before any reactor power is provided. This produces
enough heat to make steam and initiate roll off of the steam turbine.
Obviously, the volume of steam is very low.
Now you can give your stepdaughter a little test. Not sure this all made
sense to me in school...had to do a lot of practical work with it first.
- -Larry Price
73 Painted Desert
>that Wes has the info cited above. Thats why I got the pump from
Cinnabar.
>There are many gurus who say the paddle pump is not the right one.
The
>only one we want is the solid disc pump. Do you have any thoughts
that
>you would be willing to share with us on this subject. Anything
form
>horsepower to flow rate would be accepted. I only know what I think
I know
>not what the numbers say. We need you engineer types to read those
>tea leaves for us.
Arch
First I better give you the definition of an "ENGINEER"
An engineer is one who passes as an exacting expert on the strength of being
able to turn out with prolific fortitude, strings of incomprehensible
formula, calculated with microscopic precision from extremely vague
assumptions which are based on debatable incomplete experimentation carried
out with instruments of problematic accuracy by persons of doubtful
reliability and rather dubious mentality, with the particular anticipation
of disconcerting and annoying everyone outside their own fraternity.
With that disclaimer out in the open, I will attempt to help a little more.
A pump with a solid disc (called a "closed impeller") is typically more
efficient than a paddle impeller (called and "open impeller"). The reason
is that there is less slippage of the fluid around the vanes....everything
else being equal...such as clearances, diameter, number of vanes, etc.
So, if all other factors were equal, and one pump had a disc/closed impeller
and another had a paddle/open impeller.....the disc/closed impeller pump
would be more efficient. That means that the horsepower required per gallon
pumped would be less. Efficiency in the GMC application is really not that
important. I think the goal is the "correct" flow for an RPM band. This
could be achieved by pumps of various efficiencies. A low efficiency pump
may not need a flow restrictor, and will use more HP than a higher
efficiency pump. A disc/closed impeller probably flows water better than an
open/paddle impeller at low RPMs (like idle). At cruising RPMs, the flow
difference may be imperceptible. The larger the impeller the greater the
flow for a given RPM (again with all other factors equal). The number of
blades/vanes for a given diameter will probably affect efficiency more than
flow. The "ideal" water pump for the desired service conditions would
probably be a closes impeller with running clearance of about 0.010" and
have precisely contoured and machined vanes in the impellers and flow
straighteners in the volute (casing). However, this would make it a $1,000
- - $ 5,000 pump.
Conclusion: whatever pump configuration(s) that provides the "correct" flow
at the desired RPM band without cavitation are good.
I met the owner of FLOWKOOLER automotive water pumps a few years ago. They
manufacture high performance water pumps. I think that they do this by
upgrading standard pumps. I purchased one for my Ford pick-up a few years
ago. Being an engineer type, I had to take it apart to "inspect" it before
installing. This particular one was "upgraded" by adding a sheet metal disc
to a paddle type impeller. Their general pump flow curve indicated 100%
more flow at 900 RPM, and 20% more at 2000 RPM. So,
if keeping temperature down while setting/idling is an issue, the closed
impeller is probably better. At cruising RPM either is probably OK. I will
try to pick the brain of the owner of FLOWKOOLER in the future....he invited
me for a tour of his facility.
- -Larry (aka engineer type)
73 Painted Desert
>This jibes more or less with what I had
>always heard and surmised. Still wish I understood exactly what
happens to
>the water molecules during shutoff that lowers the power absorbed,
but I
>accept that it happens. Oh well, my 19 yr. old stepdaughter is an
>engineering student at CU, maybe she can explain it in a semester
or two. ;-)
>Rick Staples
Hey Rick....you gave me a pretty easy one here.
The HP going into the pump (energy) is converted to heat energy and raises
the temperature of the water. It friction heats the water by "beating" it
with the impeller vanes instead of pumping it. So, the water molecules just
absorb the energy as heat rather than as mass flow energy. Most centrifugal
pumps that have a valve to shut off the discharge have a minimum flow bypass
line to provide the minimum acceptable flow to prevent overheating. Large
industrial centrifugal pumps are started at shutoff (if possible) to
minimize starting HP. A good example of friction heating of fluid by a pump
is a nuclear power reactor. Upon start-up, water in the system is heated by
running the reactor recirculation pumps (huge vertical "GMC water pumps") in
a closed loop mode before any reactor power is provided. This produces
enough heat to make steam and initiate roll off of the steam turbine.
Obviously, the volume of steam is very low.
Now you can give your stepdaughter a little test. Not sure this all made
sense to me in school...had to do a lot of practical work with it first.
- -Larry Price
73 Painted Desert
