[dvldoc]

Here's some interesting info on pump pressure vs nozzle size.

We did this on 4 nozzle sizes on our bench test pump which is a shurflo with the factory pressure switch bypass option.


There is no pressure switch to effect the on and off of the pump. Wtithout the pressure snubber to get a accurate pressure reading just going off the gauge shows almost 200psi with the needle bouncing like mad. Not a good way to test.

Other factors that effect output pressure

Changes in the fluid temperature will change the viscosity & density of the fluid.
Fluid flow in pipes is affected by many different factors:
The viscosity, density, and velocity of the fluid.
Changes in the fluid temperature will change the viscosity & density of the fluid.
The length, inner diameter, and in the case of turbulent flow, the internal roughness of the tube.
The position of the supply and discharge containers relative to the pump position.
The addition of rises & falls within the tube layout.
The number & types of bends in the tube layout.
The number & types of valves, & other fittings, in the tube layout.

Fluids in motion are subjected to various resistances, which are due to friction. Friction may occur between the fluid & the pipe work, but friction also occurs within the fluid as sliding between adjacent layers of fluid takes place. The friction within the fluid is due to the fluid’s viscosity.

When fluids have a high viscosity, the speed of flow tends to be low, and resistance to flow becomes almost totally dependant on the viscosity of the fluid. This condition is known as ‘Laminar flow’.




See new post for new pump numbers.

Remember these pumps flow ratings are based on 3/8 ID hose with a nozzle mainly for sprayer tanks.

So this says one thing it doesn't matter what psi your pumps output is. Your hose and nozzle size effect the pressure. So if your calculating your flow directly off the pumps pressure rating it's not going to be accurate.

If you have a pump pressurizing the water, then the pressure it is able to
maintain will drop with larger holes, because more water will be escaping.
(More flow at less pressure)

The Venturi effect is a special case of the Bernoulli effect, in the case of fluid or air flow through a tube or pipe with a constriction in in it. The fluid must speed up in the restriction, reducing its pressure and producing a partial vacuum via the Bernoulli Effect.


So there is no black and white pressure, The only way to know is with a gauge. So even if you have a pump that is supposed to do 150psi it's got to get over all these factors first.


Fact 1, The max output pressure on all these pumps is around 60psi open flow and that is dependent on hose size the smaller the higher it is.

It is the hose size and nozzle restriction that causes higher output pressures seen on a gauge. So if your running a open hose the pressure switch will never be effected the pump will just run. If you have a restiction such as a nozzle that is under the set pressure it will never be effected.


Fact 2. The pressure switch on the top of the pump has jack didly squat to do with max pressure. It increases the pressure switches turn off point in 5psi increments give or take a few psi. The pressure switch simple turns the pump off at the pre-set point. By raising this you allow higher psi output and less pulsing.

Here's the break down on the pressure switches
The pressure switches have a differential on off point of 15 to 18psi.
so a un-molested 100psi pump will cut off at 100psi and turn back on at 85psi.

Fact 3. All the 8000 series pumps have a internal thearmal overload switch if the pump reaches a certain temp it will shut off and not come back on until it has cooled. Do not bypass the factory pressure switch on the pump if your running it for more than 45 minutes non stop. It heats up the switch and can runnin it. This little factoid only really effects turbo disel guys. They just turn the adjustment bolt on the pump 7 times clockwise and it will give you the maximum pressure differential of the pump and the demand switch


Fact 4. Bypass modle pumps run at almost the same PSI as all others. The only difference is they have a few extra componets internally. A spring and a few screws and that's it.


Fact 5. 150psi pumps have a slightly larger motor due to the new 8mm bearing they have. So they are a bit more rugged and physically larger. We find them a bit bulky for most applications where space is a issue.

So bottom line all these pumps put out around the same max pressure. Psi output of the pump is a direct result of the size of nozzle restriction is in place. The pressure switch simply shuts the pump on and off when it hits that set pressure it has nothing to do with max output of the pump. All pressure switches can be adjusted and are designed to do so.



You can get a 150psi pressure switch for $14 from shurflo. The only difference is a slightly larger and stiffer spring. That's it