How do I calculate a pumps psi output?

In summary, a 3.5 horsepower centrifugal pump can only lift a 687 gallon tank up to 12.5 feet, and the pump itself has a .036 horsepower rating.
  • #1
jimhebert
29
0
I have a pump that puts out 396 gal/hr of water. The output pipe on the pump is 9/16 inch in diameter. Is there a way to calculate the psi?
 
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  • #2
It can be done but it isn't easy: you have to add up the pressure losses of all of the components of the piping system
 
  • #3
Ok, I thought maybe there was a simple formula that could be applied. Thank You anyway.

On second thought, the piping is the same size as the outlet and it is only about 6 feet long, but the pump will be pumping the water up. It's for an aquarium.
 
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  • #4
jimhebert said:
I have a pump that puts out 396 gal/hr of water. The output pipe on the pump is 9/16 inch in diameter. Is there a way to calculate the psi?

Pumps have a charcteristic that they will produce a certain flowrate at a certain head. I assume you mean 396 gal/hr at zero head. As the head is increased by adding more pipe to the pump exit, the flowrate decreases, up to a point where there will be a maximum pressure at the pump but no flow. By plotting several points on a graph of flow versus head, one obtains a pump characteristic curve.

The system curveon the other hand of all the losses in the pipe is more difficult to obtain as Russ mentioned.

The intersection of the system curve with the pump characteristic curve will give you the point at which the pump is operating.

On second thought, the piping is the same size as the outlet and it is only about 6 feet long, but the pump will be pumping the water up. It's for an aquarium.

The 6 foot pipe section upwards will give only the elevation head loss for the system curve.
 
  • #5
The 396 gall/hr is the flow rate with the 6 feet of head according to the chart that you are mentioning. So I guess it is still not possible to calculate the psi?
 
  • #6
We can roughly approximate the head if we know the pump input power and the efficiency.

The efficiency of pumps are usually between 60% and 70% and of the driver ( motor) is above 90%.

The output power of the the pump is the flow rate times head.

If the driver is running with for example 50 W, for the flow rate of 396 gal/hr ( about 0.0004 m3/sec), we will get

[itex]\Delta P=\frac{50\times 0.65 \times 0.9}{0.0004}=0.7 KPa[/itex]

which is about 7 meters of water .
 
  • #7
These specs may help in your calculations. The pump is a 3.5 horsepower.

The watts are 68, voltage =120, amps=.7
The Q max GPH = 687 gph
The Q min GPH = 449 gph
Head max =12.5 feet
 
  • #8
jimhebert said:
These specs may help in your calculations. The pump is a 3.5 horsepower.

The watts are 68, voltage =120, amps=.7
The Q max GPH = 687 gph
The Q min GPH = 449 gph
Head max =12.5 feet

The pump horsepower seems too much! According to your number, your pump can do more work as 3 horses can do. Such a pump needs a powerful driver not a 68 watt one.
 
  • #9
You mean it is not a 3.5 HP pump as the specifications say? According to your calculations, you believe it to be a 3 HP...Correct?
 
  • #10
jimhebert said:
You mean it is not a 3.5 HP pump as the specifications say? According to your calculations, you believe it to be a 3 HP...Correct?

I expected a much less hp. Something like 0.1 HP. Or perhaps its 3/5 hp rather than 3.5 hp.

See this online calculator http://www.engineeringtoolbox.com/pumps-power-d_505.html
 
  • #11
In the calculator I entered q=687, and h=12.15 and shaft bph =3.52
 
  • #12
jimhebert said:
In the calculator I entered q=687, and h=12.15 and shaft bph =3.52


The calculator gets the flow in units of gallon/minute. Yours is per gallon/hour
 
  • #14
That's a picture of an aquarium pump not a lawn sprinkler pump.
That much power would wreck an aquarium.
HP must mean something else. Probably "High Performance".

Figure the power it takes to lift the weight of 687 gallons of water twelve and a half feet in an hour.
F X D / T .
(8.3 X 687) X 12.5 / 3600 = 19.8 ft-lbs/sec = .036 hp by my back of envelope, ~26 watts.



To OP's question about discharge pressure - it's given in your spec.
Centrifugal Pump "head" is the discharge pressure given in units " height of fluid flowing."
Convert 12.5 feet of water to PSI.
Were the pump instead pumping mercury, its discharge would be 12.5 feet of mercury and input power would be much higher.
 
  • #15
Found its discharge curve..

http://www.f3images.com/IMD/MD_images/aquarium/Sicce_Syncra_Silent.jpg

Sicce_Syncra_Silent.jpg


i'd say 3.5 meters is about all the useful lift you'll get.

Credit is due this online store for posting the information. I like an outfit with that attention to detail.

http://www.marinedepot.com/ps_viewi...tm_campaign=mdcseshopping2&utm_content=XJ1141
 
  • #16
I bought this pump in pet shop and they had one in use in an aquarium. I do want to use it in a large tank. I would still like to know the approximate PSI output curve if possible.

The posted curve is not plotted correctly. The column with all the Syncras needs to be lifted up 2 increments and the H/m shifted to the right.
 
  • #17
jimhebert said:
I bought this pump in pet shop and they had one in use in an aquarium. I do want to use it in a large tank. I would still like to know the approximate PSI output curve if possible.

The posted curve is not plotted correctly. The column with all the Syncras needs to be lifted up 2 increments and the H/m shifted to the right.

The plot seems fine. The column of Syncras is there just tell you ,by color , that which curve is for which pump. It has nothing with the vertical axis.

3.5 meters is not enough for your purpose? by the way, isn't pressure in unit of meters/ft of water easier to understand? I wonder why you keep asking the psi.
 
  • #18
I want to attach another device to the pump and it requires a certain psi to function properly.
 
  • #19
jimhebert said:
I want to attach another device to the pump and it requires a certain psi to function properly.

Thanks for the clarification.

The chart gives you the pressure just at the discharge of the pump. If after the pump, your pipe goes upward, The pressure on the top is less than that. Add friction too, though friction can be reduced to a small value. If the pipe goes horizontally, The psi of the end of the pipe is something between 5.0 and 6.0 psi. If the pipe goes upward, reduce 1.5 psi per meter from the value of horizontal case.
 
  • #20
Thank you for resolving this problem. As you said the chart gives you the answer automatically if you know how to interpret it correctly. That's all I guess and have a good day.
 

1. How do I determine the psi output of a pump?

To calculate the psi output of a pump, you will need to know the pump's flow rate and the pump's total head. The formula for psi output is psi = (flow rate * total head) / (4.9 * pump efficiency).

2. What is the formula for calculating psi output?

The formula for calculating psi output is psi = (flow rate * total head) / (4.9 * pump efficiency), where flow rate is measured in gallons per minute (GPM), total head is the vertical distance the pump can move water, and pump efficiency is expressed as a decimal between 0 and 1.

3. Can I use the same formula for all types of pumps?

No, the formula for calculating psi output may vary depending on the type of pump. For example, a centrifugal pump may use a different formula than a positive displacement pump. It is important to consult the manufacturer's specifications for the specific pump you are using.

4. How do I determine the pump's flow rate?

The pump's flow rate can be determined by measuring the amount of water that the pump can move in a given amount of time. This is typically measured in gallons per minute (GPM) or liters per minute (LPM). You can also refer to the manufacturer's specifications for the pump's flow rate.

5. What is pump efficiency and how do I know the value to use in the formula?

Pump efficiency is a measure of how well the pump is able to convert energy into water flow. It is expressed as a decimal between 0 and 1, with 1 being the most efficient. The pump efficiency can usually be found in the manufacturer's specifications, or it can be estimated based on the type and age of the pump.

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