[steve m]

can someone tell me why a pump rated at 100psi pumps less water per minute than a pump raed at 60psi  -  ei, 100psi 4litres per minute and 60psi 7litres per minute

[chris@c.m.s]

Pressure and flow rate are 2 totally different things.

[steve m]

maybe I'm looking at it wrong but if a pump is pumping at 100psi, the water will fill a litre container faster than a 60psi one, so surely the first one must pump more per minute. Both the inlet and outlet are the same??

[chris@c.m.s]

I'm not completely sure myself but there is a difference and that must be within the pump I guess,
its an interesting question though, and you would assume that at height a 100 psi pump will put more water on the glass than a 60 psi one    Hmmm thinking about it that  must be the reason for the increased pressure  :

[Alex Gardiner]

The PSI rating is purely to do with the setting of the pressure switch. Higher rated pressure switches are usually used when the pumps needs to pump water further/higher.

The flow rate is to do with the mechanics of the pump, it's diaphragms, speed etc.

[Jon-scwindows]

its just because they are different sizes, pumping at 100psi sounds like more, but if it has a smaller outlet then its going to pump less water than a pump pumping at 100 with a larger outlet, its like if there was a 100 psi pump the size of a houshold bin, its going to pump more water than a 100psi pump like the sureflow,
if the 60 psi pump has a higher flow rate, then its pumping the water faster, but at a lower pressure.
a 100 psi pump can produce that pressure at a lower speed because of its size. The 60psi pump produces 60psi but it has to run faster to get there, and as the outlets are the same size the smaller diaphram in the pump has to run faster.

[alanwilson]

look at it this way - the shurflo pumps in our vans are 100psi 5.2ltr/min but our sub pump is prob only about 20psi but pumps @ 320ltr/min

As has already been said, pressure and flow rate are completely different.

[steve m]

so, the next question is can I buy a 40psi pump that pumps at 7lpm and put a bigger pressure switch on it???. One for Alex I fear

[Alex Gardiner]

so, the next question is can I buy a 40psi pump that pumps at 7lpm and put a bigger pressure switch on it???. One for Alex I fear

Why would you want to buy one at 40 psi and then put a bigger pressure switch on it when you can already buy a 7 lpm pump that has a large pressure switch?  The Flojet 100 psi has a flow rate of 7.6 lpm.

[Alex Wingrove]

i agree i like the flojet, perfect with microbore,

[steve m]

basically a 40psi pump will sell for £35.00, and the flojets are an arm and a leg, and I only want it for a spare in the van juust in case

[Alex Gardiner]

It's finding a 40 psi pump with enough flow rate that has the ability to take a bigger pressure switch. 

[steve m]

I found one with a flow rate of seven litres per minute, thats what started this thread

[alanwilson]

you can always screw the grub screw down tighter - thats how they adjust the pressure switch setting.

[Conflagration2000]

When I was a brave Firefighter each branch nozzle had an optimum pressure. For instance a 5/8" nozzle was 60psi if I remember correctly. Now if the pump pressure was raised to 100 psi then the flow out of the nozzle would actually decrease and you would notice that instead of a nice clean jet of water it would start to peel off and turn into a spray. I think a lot of it is to do with back pressure and frictional loss within the hose.

[Jon-scwindows]

remember to tighten up the casing if you unscrew the pressure switch part otherwise it leaks like mad

[steve m]

all I was thinking was changing the pressure from 40psi to 60psi, and where can I get a new pressure switch from?

[Alex Gardiner]

all I was thinking was changing the pressure from 40psi to 60psi, and where can I get a new pressure switch from?

As I said a few posts ago it's finding a pump that you can upgrade the switch on. It seems only the expensive makes have a wide choice of pressure switches.