radiator caps, cooling system pressure

"MLD" > wrote in message ...
>
> "Guv Bob" > wrote in message
> m...
> "MLD" > wrote in message ...
> >
> > > wrote in message
> > ...
> > > On Sun, 21 Apr 2013 18:50:29 -0700 (PDT), "
> > > > wrote:
> > >
> > >>On Apr 21, 6:11 pm, Tony Hwang > wrote:
> > >>> Ashton Crusher wrote:
> > >>> > I was thinking of putting a higher pressure cap on one of my cars to
> > >>> > increase the factor of safety against boiling. Looking thru the web
> > >>> > for info on the likelihood of changing from 7 psi to 13 psi causing
> > >>> > leaks I found little on that issue but did find a couple references
> > >>> > to
> > >>> > the pressures created by the water pump. One site boasts of a 19
> > >>> > PSI,
> > >>> > $25 cap to get you thru your "hard driving".
> > >>> >http://www.mishimoto.com/mishimoto-h...tor-cap-13-bar....
> > >>> > Thought I'd see if anyone else has heard of this. The claim was that
> > >>> > the water pump could create over 30 PSI of pressure. Since that is
> > >>> > double the normal operating pressure of most modern cars I find it
> > >>> > hard to believe. If the system was at full 15 psi of pressure while
> > >>> > the car is idling and then your floored it and ran it up to near
> > >>> > redline and created another 30psi of additional pump pressure, or
> > >>> > even 10 psi of additioingnal pressure downstream at the radiator
> > >>> > cap,
> > >>> > you
> > >>> > would immediately cause the system to have to vent to the overflow
> > >>> > to
> > >>> > relieve this higher pressure. I've never seen a car vent due to me
> > >>> > revving the engine up while I'm working on it. Thoughts?????
> > >>>
> > >>> Hi.
> > >>> There is a over flow bottle for coolant/anti-freeze. Ever
> > >>> cleaned/flushed your rad. and maintain proper level of
> > >>> coolant/anti-freeze in your rad.? If the car is old, messing with cap
> > >>> can spring
> > >>> a leak.- Hide quoted text -
> > >>>
> > >>> - Show quoted text -
> > >>
> > >>AMEN!
> > > A water pump cannot produce system pressure because it just moves
> > > water from one side of the pump to the other. Expansion due to heat is
> > > what builds pressure..
> >
> > I guess you need to know how a centrifugal pump works. Pressure rise
> > across the pump is function of the square of its speed. Double the pump
> > speed and the delta P across the pump increases 4X. Expansion due to
> > heat
> > will increase system pressure if it is in a closed system. If a fluid can
> > expand without being constrained---no significant change in pressure.
> > MLD
>
> Well, I give each of you half credit. LOL! At a certain RPM, the pump head
> (outlet-inlet pressure) and flow rate are both are fairly indept of the
> coolant temperature as long as the coolant stays a liquid (normal condition)
> when going through the pump. The engine heat raises the coolant temperature
> and the pressure (remember this from skool... PV=nRT), but (and this is a
> big butt) as long as the pump turns at the same RPM, the head should stay
> about the same.
>
> FWIW, here's a decent drawing of a water pump cross-section
> http://assets.hemmings.com/story_image/83720-500-0.jpg
>
> A couple of comments--PV=nRT is an equation used in gas flow calculations
> not when the fluid is a liquid. Don't understand where you are coming from.

As the engine temperature rises, tiny gas bubbles start to form on the walls of the cooling cavities. The liquid changing to gas causes the pressure to increase. When the fluid is cold, the bubbles are condensed back into liquid right away and there is little pressure increase. As the coolant temp rises, it takes longer for them to condense, the volume of gas increases and the pressure increases.

> Just for the record, at constant speed the pressure rise across a
> centrifugal pump does not remain constant. Typically, there is a droop
> (loss of delta P) as the pump flow demand increases. Relatively
> insignificant at first but if the flow demand gets large enough, then the
> Pump Delta P can drop significantly. Flow demand is dictated by the
> characteristics of the the system in question--that is, how the delta P vs
> Flow of the system (line losses etc.) matches up with the delta P vs flow of
> the pump. Where the two intersect will be the operating point of the
> System. The idea is to match them so that the intersection takes place
> where the droop in pump deta P is relatively insensitive to flow demand.
> MLD

On 4/30/2014 6:15 PM, MLD wrote:
>
> > wrote in message
> ...
>> On Sun, 21 Apr 2013 18:50:29 -0700 (PDT), "
>> > wrote:
>>
>>> On Apr 21, 6:11 pm, Tony Hwang > wrote:
>>>> Ashton Crusher wrote:
>>>> > I was thinking of putting a higher pressure cap on one of my cars to
>>>> > increase the factor of safety against boiling. ...

....

>>>> > Thought I'd see if anyone else has heard of this. The claim was that
>>>> > the water pump could create over 30 PSI of pressure. Since that is
>>>> > double the normal operating pressure of most modern cars I find it
>>>> > hard to believe. If the system was at full 15 psi of pressure while
>>>> > the car is idling and then your floored it and ran it up to near
>>>> > redline and created another 30psi of additional pump pressure, or
>>>> > even 10 psi of additioingnal pressure downstream at the radiator
>>>> cap, > you
>>>> > would immediately cause the system to have to vent to the overflow to
>>>> > relieve this higher pressure. I've never seen a car vent due to me
>>>> > revving the engine up while I'm working on it. Thoughts?????
....

What the limit is of how much pressure the water pump can produce is
based on the pump design and I really don't know what those values
typically might be. But, the pressure in the system is controlled by
the pressure cap. There's a very good description at the following link...

<http://books.google.com/books?id=xLx...136&lpg=PA136&

dq=does+radiator+cap+control+radiator+pressure&sou rce=bl&ots=--_LIFglKt&

sig=vhm95_RJG8vWT6iJMsaY-3OAGmM&hl=en&sa=X&ei=FdNjU-SuJfP7yAGho4CwCQ&

ved=0CIgBEOgBMAg#v=onepage&

q=does%20radiator%20cap%20control%20radiator%20pre ssure&f=false>

--

"dpb" > wrote in message ...
> On 4/30/2014 6:15 PM, MLD wrote:
>>
>> > wrote in message
>> ...
>>> On Sun, 21 Apr 2013 18:50:29 -0700 (PDT), "
>>> > wrote:
>>>
>>>> On Apr 21, 6:11 pm, Tony Hwang > wrote:
>>>>> Ashton Crusher wrote:
>>>>> > I was thinking of putting a higher pressure cap on one of my cars to
>>>>> > increase the factor of safety against boiling. ...
>
> ...
>
>>>>> > Thought I'd see if anyone else has heard of this. The claim was that
>>>>> > the water pump could create over 30 PSI of pressure. Since that is
>>>>> > double the normal operating pressure of most modern cars I find it
>>>>> > hard to believe. If the system was at full 15 psi of pressure while
>>>>> > the car is idling and then your floored it and ran it up to near
>>>>> > redline and created another 30psi of additional pump pressure, or
>>>>> > even 10 psi of additioingnal pressure downstream at the radiator
>>>>> cap, > you
>>>>> > would immediately cause the system to have to vent to the overflow
>>>>> > to
>>>>> > relieve this higher pressure. I've never seen a car vent due to me
>>>>> > revving the engine up while I'm working on it. Thoughts?????
> ...
>
> What the limit is of how much pressure the water pump can produce is based
> on the pump design and I really don't know what those values typically
> might be. But, the pressure in the system is controlled by the pressure
> cap. There's a very good description at the following link...
>
> <http://books.google.com/books?id=xLx...136&lpg=PA136&
>
> dq=does+radiator+cap+control+radiator+pressure&sou rce=bl&ots=--_LIFglKt&
>
> sig=vhm95_RJG8vWT6iJMsaY-3OAGmM&hl=en&sa=X&ei=FdNjU-SuJfP7yAGho4CwCQ&
>
> ved=0CIgBEOgBMAg#v=onepage&
>
> q=does%20radiator%20cap%20control%20radiator%20pre ssure&f=false>
>
> --


30 psi is putting it mildly....

"mike" > wrote in message
...
> On 5/1/2014 4:46 PM, MLD wrote:
>>
>> "mike" > wrote in message
>> ...
>>> On 5/1/2014 9:39 AM, MLD wrote:
>>>>
>>>> "Guv Bob" > wrote in message
>>>> m...
>>>> "MLD" > wrote in message
>>>> ...
>>>>>
>>>>> > wrote in message
>>>>> ...
>>>>> > On Sun, 21 Apr 2013 18:50:29 -0700 (PDT), "
>>>>> > > wrote:
>>>>> >
>>>>> >>On Apr 21, 6:11 pm, Tony Hwang > wrote:
>>>>> >>> Ashton Crusher wrote:
>>>>> >>> > I was thinking of putting a higher pressure cap on one of my
>>>>> cars to
>>>>> >>> > increase the factor of safety against boiling. Looking thru
>>>>> the >>> > web
>>>>> >>> > for info on the likelihood of changing from 7 psi to 13 psi
>>>>> >>> > causing
>>>>> >>> > leaks I found little on that issue but did find a couple
>>>>> references >>> > to
>>>>> >>> > the pressures created by the water pump. One site boasts of a 19
>>>>> >>> > PSI,
>>>>> >>> > $25 cap to get you thru your "hard driving".
>>>>> >>>
>>>>> >http://www.mishimoto.com/mishimoto-h...tor-cap-13-bar....
>>>>>
>>>>> >>> > Thought I'd see if anyone else has heard of this. The claim was
>>>>> that
>>>>> >>> > the water pump could create over 30 PSI of pressure. Since
>>>>> that is
>>>>> >>> > double the normal operating pressure of most modern cars I
>>>>> find it
>>>>> >>> > hard to believe. If the system was at full 15 psi of pressure
>>>>> >>> > while
>>>>> >>> > the car is idling and then your floored it and ran it up to near
>>>>> >>> > redline and created another 30psi of additional pump pressure,
>>>>> >>> > or
>>>>> >>> > even 10 psi of additioingnal pressure downstream at the radiator
>>>>> >>> > cap,
>>>>> >>> > you
>>>>> >>> > would immediately cause the system to have to vent to the
>>>>> overflow >>> > to
>>>>> >>> > relieve this higher pressure. I've never seen a car vent due
>>>>> to me
>>>>> >>> > revving the engine up while I'm working on it. Thoughts?????
>>>>> >>>
>>>>> >>> Hi.
>>>>> >>> There is a over flow bottle for coolant/anti-freeze. Ever
>>>>> >>> cleaned/flushed your rad. and maintain proper level of
>>>>> >>> coolant/anti-freeze in your rad.? If the car is old, messing
>>>>> with >>> cap
>>>>> >>> can spring
>>>>> >>> a leak.- Hide quoted text -
>>>>> >>>
>>>>> >>> - Show quoted text -
>>>>> >>
>>>>> >>AMEN!
>>>>> > A water pump cannot produce system pressure because it just moves
>>>>> > water from one side of the pump to the other. Expansion due to
>>>>> heat is
>>>>> > what builds pressure..
>>>>>
>>>>> I guess you need to know how a centrifugal pump works. Pressure rise
>>>>> across the pump is function of the square of its speed. Double the
>>>>> pump
>>>>> speed and the delta P across the pump increases 4X. Expansion due to
>>>>> heat
>>>>> will increase system pressure if it is in a closed system. If a fluid
>>>>> can
>>>>> expand without being constrained---no significant change in pressure.
>>>>> MLD
>>>>
>>>> Well, I give each of you half credit. LOL! At a certain RPM, the pump
>>>> head (outlet-inlet pressure) and flow rate are both are fairly indept
>>>> of
>>>> the coolant temperature as long as the coolant stays a liquid (normal
>>>> condition) when going through the pump. The engine heat raises the
>>>> coolant temperature and the pressure (remember this from skool...
>>>> PV=nRT), but (and this is a big butt) as long as the pump turns at the
>>>> same RPM, the head should stay about the same.
>>>>
>>>> FWIW, here's a decent drawing of a water pump cross-section
>>>> http://assets.hemmings.com/story_image/83720-500-0.jpg
>>>>
>>>> A couple of comments--PV=nRT is an equation used in gas flow
>>>> calculations not when the fluid is a liquid. Don't understand where
>>>> you
>>>> are coming from. Just for the record, at constant speed the pressure
>>>> rise across a centrifugal pump does not remain constant. Typically,
>>>> there is a droop (loss of delta P) as the pump flow demand increases.
>>>> Relatively insignificant at first but if the flow demand gets large
>>>> enough, then the Pump Delta P can drop significantly. Flow demand is
>>>> dictated by the characteristics of the the system in question--that is,
>>>> how the delta P vs Flow of the system (line losses etc.) matches up
>>>> with
>>>> the delta P vs flow of the pump. Where the two intersect will be the
>>>> operating point of the System. The idea is to match them so that the
>>>> intersection takes place where the droop in pump deta P is relatively
>>>> insensitive to flow demand.
>>>> MLD
>>>>
>>> Riddle me this.
>>> In a CLOSED system FILLED with INCOMPRESSIBLE liquid, the pressure is
>>> whatever
>>> the pressure is.
>>> The pump can't put more pressure on the output side than is on the input
>>> side because it's a CLOSED system FILLED with INCOMPRESSIBLE liquid.
>>>
>>> Do pump principles applied to OPEN systems really apply?
>>
>> Don't understand either of your comments. Could you expand your
>> explanations so they make some sense?
>> Do you know what happens if you dead end a centrifugal pump (Zero flow)
>> while its running?? The discharge pressure might not change but you
>> better be prepared to see the fluid temperature skyrocket.
>> You seem to to make a big point out of INCOMPRESSIBLE fluid. Got some
>> news for you, Ready---fluids, aka liquids, are not INCOMPRESSIBLE!!!
>> Have you ever heard of "Bulk Modulus", entrained air or compressible
>> flow as they apply to liquids?
>> Do you know what would happen to the pressure in a closed system if the
>> fluid temperature (say water) was increased but the fluid was not able
>> to expand due to the closed (or fixed) system volume?
>> Hint: Delta P=(BM) x (Delta V)/V
>> Clue: Pressure can increase up to the thousands! Want to try and
>> conduct your own experiment? Close the water inlet shut off valve in
>> your house. Keep all faucets closed and of course, lock the hot water
>> tank relief valve so that it doesn't open. Now just crank up the
>> temperature of your water heater. This ought to seek out your system's
>> weak link.
>> MLD
>>
>>
> Can't argue with your theory. Problem is that it doesn't apply here
> in any significant amount.
> If the pressure exceeds the cap pressure, it vents.
> The pump didn't add the pressure. In your scenario, the pump added
> heat.
> So, get back to the topic. In a closed car cooling system under normal
> operation
> can the pressure on the output side of the pump significantly exceed
> the pressure on the input side?
>
> I think we can exclude any vaporization of the liquid leading to excess
> pressure. If it did, it would vent and, eventually, there'd be no more
> liquid to pump.
>
> But thank you for the clue and the hint and the nitpicking.



Once more---A centrifugal pump--that's what is in your car--the pump
discharge pressure is a function of the pump speed squared. Once the
thermostat opens there is a flow path from pump to radiator back to the pump
inlet. Other than a slight droop in pressure due to the flow demand, the
pressure rise across the pump basically constant. Obviously, no venting
occurs as long as the pressure at the radiator is less then the cap pressure
setting. Pressure at the radiator is established by whatever line loses
there are between the pump discharge and radiator. Venting occurs because
as the coolant temperature increases it's volume will also increase. Why??
Density=Weight/Volume.
Density decreases as temperature increases. Since the weight of the coolant
doesn't change, it's the volume that does.
As the coolant expands, the pressure in the system increases (remember,
trapped volume aka closed system) and when the pressure gets to the cap
setting (won't take long), the cap opens and the fluid goes into the
overflow bottle. If the radiator cap didn't open--whole new
scenario--things would break!!
If this doesn't answer your questions, suggest you do a bit of reading on
your own.
MLD

On Fri, 2 May 2014 00:08:20 -0400, "Rick" >
wrote:

>
>"mike" > wrote in message
...
>> On 5/1/2014 4:46 PM, MLD wrote:
>
>
>> operation
>> can the pressure on the output side of the pump significantly exceed
>> the pressure on the input side?
>
>
>
>Yes, and it looks like a lot of you have no idea how much it can, and does.
The difference in pressure across the pump is equal to the difference
in pressure across the radiator. Suction on one side, pressure on the
other. A matter of a few psi with a good rad and the thermostat open.
The pump is not capable of producing very high pressures.. The
pressure on the low side can be up to 5 psi below nominal, and on the
high side as much as 5psi above no

On Fri, 02 May 2014 00:28:35 -0700, mike > wrote:

>On 5/1/2014 9:08 PM, Rick wrote:
>>
>> "mike" > wrote in message
>> ...
>>> On 5/1/2014 4:46 PM, MLD wrote:
>>
>>
>>> operation
>>> can the pressure on the output side of the pump significantly exceed
>>> the pressure on the input side?
>>
>>
>>
>> Yes, and it looks like a lot of you have no idea how much it can, and does.
>>
>I'd like to hear the rationale in a closed system.
Restriction to flow affects the "head" of the pump. No restriction,
no head pressure. A good water pump may produce a 5 psi head, and draw
an equivalent depression on the low side of the pump for a maximum
pressure differential of 10psi - but that is a "blueprinted" pump at
optimal speed with an adequately restrictive radiator.

Real world numbers are generally quite significantly less. Measured
3psi on BMW 328 just this week at 3000 RPM. Above and below 3000 it
dropped off. That was with diluted coolant (about 20-25% glycol) due
to having just repaired a leak and having the normal "fun" bleeding
all the air out of the nasty little Kraut!!

On Thu, 01 May 2014 17:05:57 -0700, mike > wrote:

>On 5/1/2014 4:36 PM, Ashton Crusher wrote:
>> On Thu, 01 May 2014 12:59:51 -0700, mike > wrote:
>>
>>> On 5/1/2014 9:39 AM, MLD wrote:
>>>>
>>>> "Guv Bob" > wrote in message
>>>> m...
>>>> "MLD" > wrote in message ...
>>>>>
>>>>> > wrote in message
>>>>> ...
>>>>>> On Sun, 21 Apr 2013 18:50:29 -0700 (PDT), "
>>>>>> > wrote:
>>>>>>
>>>>>>> On Apr 21, 6:11 pm, Tony Hwang > wrote:
>>>>>>>> Ashton Crusher wrote:
>>>>>>>>> I was thinking of putting a higher pressure cap on one of my
>>>>> cars to
>>>>>>>>> increase the factor of safety against boiling. Looking thru the web
>>>>>>>>> for info on the likelihood of changing from 7 psi to 13 psi causing
>>>>>>>>> leaks I found little on that issue but did find a couple
>>>>> references >>> > to
>>>>>>>>> the pressures created by the water pump. One site boasts of a 19
>>>>>>>>> PSI,
>>>>>>>>> $25 cap to get you thru your "hard driving".
>>>>>>>>
>>>>>> http://www.mishimoto.com/mishimoto-h...tor-cap-13-bar....
>>>>>>>>> Thought I'd see if anyone else has heard of this. The claim was
>>>>> that
>>>>>>>>> the water pump could create over 30 PSI of pressure. Since that is
>>>>>>>>> double the normal operating pressure of most modern cars I find it
>>>>>>>>> hard to believe. If the system was at full 15 psi of pressure while
>>>>>>>>> the car is idling and then your floored it and ran it up to near
>>>>>>>>> redline and created another 30psi of additional pump pressure, or
>>>>>>>>> even 10 psi of additioingnal pressure downstream at the radiator
>>>>>>>>> cap,
>>>>>>>>> you
>>>>>>>>> would immediately cause the system to have to vent to the
>>>>> overflow >>> > to
>>>>>>>>> relieve this higher pressure. I've never seen a car vent due to me
>>>>>>>>> revving the engine up while I'm working on it. Thoughts?????
>>>>>>>>
>>>>>>>> Hi.
>>>>>>>> There is a over flow bottle for coolant/anti-freeze. Ever
>>>>>>>> cleaned/flushed your rad. and maintain proper level of
>>>>>>>> coolant/anti-freeze in your rad.? If the car is old, messing with cap
>>>>>>>> can spring
>>>>>>>> a leak.- Hide quoted text -
>>>>>>>>
>>>>>>>> - Show quoted text -
>>>>>>>
>>>>>>> AMEN!
>>>>>> A water pump cannot produce system pressure because it just moves
>>>>>> water from one side of the pump to the other. Expansion due to heat is
>>>>>> what builds pressure..
>>>>>
>>>>> I guess you need to know how a centrifugal pump works. Pressure rise
>>>>> across the pump is function of the square of its speed. Double the pump
>>>>> speed and the delta P across the pump increases 4X. Expansion due to
>>>>> heat
>>>>> will increase system pressure if it is in a closed system. If a fluid
>>>>> can
>>>>> expand without being constrained---no significant change in pressure.
>>>>> MLD
>>>>
>>>> Well, I give each of you half credit. LOL! At a certain RPM, the pump
>>>> head (outlet-inlet pressure) and flow rate are both are fairly indept of
>>>> the coolant temperature as long as the coolant stays a liquid (normal
>>>> condition) when going through the pump. The engine heat raises the
>>>> coolant temperature and the pressure (remember this from skool...
>>>> PV=nRT), but (and this is a big butt) as long as the pump turns at the
>>>> same RPM, the head should stay about the same.
>>>>
>>>> FWIW, here's a decent drawing of a water pump cross-section
>>>> http://assets.hemmings.com/story_image/83720-500-0.jpg
>>>>
>>>> A couple of comments--PV=nRT is an equation used in gas flow
>>>> calculations not when the fluid is a liquid. Don't understand where you
>>>> are coming from. Just for the record, at constant speed the pressure
>>>> rise across a centrifugal pump does not remain constant. Typically,
>>>> there is a droop (loss of delta P) as the pump flow demand increases.
>>>> Relatively insignificant at first but if the flow demand gets large
>>>> enough, then the Pump Delta P can drop significantly. Flow demand is
>>>> dictated by the characteristics of the the system in question--that is,
>>>> how the delta P vs Flow of the system (line losses etc.) matches up with
>>>> the delta P vs flow of the pump. Where the two intersect will be the
>>>> operating point of the System. The idea is to match them so that the
>>>> intersection takes place where the droop in pump deta P is relatively
>>>> insensitive to flow demand.
>>>> MLD
>>>>
>>> Riddle me this.
>>> In a CLOSED system FILLED with INCOMPRESSIBLE liquid, the pressure is
>>> whatever
>>> the pressure is.
>>> The pump can't put more pressure on the output side than is on the input
>>> side because it's a CLOSED system FILLED with INCOMPRESSIBLE liquid.
>>>
>>> Do pump principles applied to OPEN systems really apply?
>>
>>
>> Great Question. My original question remains unanswered .... Does the
>> water pump ADD another 10 to 30 psi internal pressure (as the sources
>> I originally was looking at claimed) and if it does, how come that
>> extra pressure, on top of the already existing 12 psi heat pressure,
>> not cause the cap to blow off from the excess pressure now totaling
>> from 20 to 40 psi? All I can think is that the pump only adds perhaps
>> 2 to 5 psi and that by the time it "gets" to the cap area, flow
>> resistance has dissipated it down to 1 or 2 psi and it has ceased to
>> be a problem. Or maybe the pump only "adds" negative pressure, i.e.
>> suction at the inlet, or some combo of all that.
>>
>It's my contention that the pump can add no pressure unless it has
>somewhere to get the water to pump.
>If it's coming from the closed system, there ain't none available
>unless you vaporize some on the source side.
>

Your comment makes no sense to me. There is always water at the
inlet to the pump if the system if full of water. You can see the
water moving if you take the cap off, at least on some systems where
it opens into the tank. Clearly the pump is pumping water, therefore
it's getting some to pump and it's certainly not as vapor.

On Fri, 02 May 2014 14:49:18 -0400, wrote:

>On Fri, 02 May 2014 00:28:35 -0700, mike > wrote:
>
>>On 5/1/2014 9:08 PM, Rick wrote:
>>>
>>> "mike" > wrote in message
>>> ...
>>>> On 5/1/2014 4:46 PM, MLD wrote:
>>>
>>>
>>>> operation
>>>> can the pressure on the output side of the pump significantly exceed
>>>> the pressure on the input side?
>>>
>>>
>>>
>>> Yes, and it looks like a lot of you have no idea how much it can, and does.
>>>
>>I'd like to hear the rationale in a closed system.
> Restriction to flow affects the "head" of the pump. No restriction,
>no head pressure. A good water pump may produce a 5 psi head, and draw
>an equivalent depression on the low side of the pump for a maximum
>pressure differential of 10psi - but that is a "blueprinted" pump at
>optimal speed with an adequately restrictive radiator.
>
>Real world numbers are generally quite significantly less. Measured
>3psi on BMW 328 just this week at 3000 RPM. Above and below 3000 it
>dropped off. That was with diluted coolant (about 20-25% glycol) due
>to having just repaired a leak and having the normal "fun" bleeding
>all the air out of the nasty little Kraut!!


Where in the system did you take that 3 psi measurement at?

On Fri, 02 May 2014 14:43:15 -0400, wrote:

>On Fri, 2 May 2014 00:08:20 -0400, "Rick" >
>wrote:
>
>>
>>"mike" > wrote in message
...
>>> On 5/1/2014 4:46 PM, MLD wrote:
>>
>>
>>> operation
>>> can the pressure on the output side of the pump significantly exceed
>>> the pressure on the input side?
>>
>>
>>
>>Yes, and it looks like a lot of you have no idea how much it can, and does.
>The difference in pressure across the pump is equal to the difference
>in pressure across the radiator. Suction on one side, pressure on the
>other. A matter of a few psi with a good rad and the thermostat open.
>The pump is not capable of producing very high pressures.. The
>pressure on the low side can be up to 5 psi below nominal, and on the
>high side as much as 5psi above no


My little 1.5 hp swimming pool pump, with similar sized centrifugal
impeller to a car, similar sized pipes as a radiator hose, and running
at a couple thousand rpm can easily produce over 25 psi if you shut
down the outlet valve. It seems likely to me that the water pump in a
150 hp car could do the same if the flow was restricted.

"MLD" > wrote in message ...
>
> > wrote in message
> ...
> > On Sun, 21 Apr 2013 18:50:29 -0700 (PDT), "
> > > wrote:
> >
> >>On Apr 21, 6:11 pm, Tony Hwang > wrote:
> >>> Ashton Crusher wrote:
> >>> > I was thinking of putting a higher pressure cap on one of my cars to
> >>> > increase the factor of safety against boiling. Looking thru the web
> >>> > for info on the likelihood of changing from 7 psi to 13 psi causing
> >>> > leaks I found little on that issue but did find a couple references to
> >>> > the pressures created by the water pump. One site boasts of a 19 PSI,
> >>> > $25 cap to get you thru your "hard driving".
> >>> >http://www.mishimoto.com/mishimoto-h...tor-cap-13-bar....
> >>> > Thought I'd see if anyone else has heard of this. The claim was that
> >>> > the water pump could create over 30 PSI of pressure. Since that is
> >>> > double the normal operating pressure of most modern cars I find it
> >>> > hard to believe. If the system was at full 15 psi of pressure while
> >>> > the car is idling and then your floored it and ran it up to near
> >>> > redline and created another 30psi of additional pump pressure, or
> >>> > even 10 psi of additioingnal pressure downstream at the radiator cap,
> >>> > you
> >>> > would immediately cause the system to have to vent to the overflow to
> >>> > relieve this higher pressure. I've never seen a car vent due to me
> >>> > revving the engine up while I'm working on it. Thoughts?????
> >>>
> >>> Hi.
> >>> There is a over flow bottle for coolant/anti-freeze. Ever
> >>> cleaned/flushed your rad. and maintain proper level of
> >>> coolant/anti-freeze in your rad.? If the car is old, messing with cap
> >>> can spring
> >>> a leak.- Hide quoted text -
> >>>
> >>> - Show quoted text -
> >>
> >>AMEN!
> > A water pump cannot produce system pressure because it just moves
> > water from one side of the pump to the other. Expansion due to heat is
> > what builds pressure..
>
> I guess you need to know how a centrifugal pump works. Pressure rise
> across the pump is function of the square of its speed. Double the pump
> speed and the delta P across the pump increases 4X. Expansion due to heat
> will increase system pressure if it is in a closed system. If a fluid can
> expand without being constrained---no significant change in pressure.
> MLD

MLD, do you know where to find a flow rate vs RPM curve for any common stock water pumps? I'm surprised I can't seem to find anything mfr spec curves at the various mfrs and parts houses. Doesn't matter what mfr or vehicle -- just any common street car single head pump.