maximum discharge pressure for 8 HP pump?

[thegeeps20]

Hi, I know I probably won't be providing enough info to answer my question, but any thoughts would be appreciated.
I'm running an 8 HP Honda engine with Monarch pump attached, pulling water from a pond. 2" discharge opening going to 3" aluminum piping, travelling about 300 ft, very slight incline to irrigation impact sprinklers(the old fashioned rainbird type) to irrigate nursery plants. I run 2 sprinklers at a time and they shoot about 60ft each. I believe the operating range of the sprinklers is 50-85PSI, flow 40-115GPM. I don't know how many GPM I'm getting now or the PSI.
My question is: could I run 2 standard garden hoses(coming off of the 3" pipe) with the sprinklers turned off without damaging the pump?
Here is some pump curve info:
-180 GPM capacity at 20' head
-100GPM at 140'
-50 GPM at 165'
-0 at 200'
Discharge Pressure in PSI at 5 ft. Lift
165GPM at 20PSI
122GPM at 50PSI
24GPM at 80 PSI

Any thoughts greatly appreciated. The reason I want to do this is the output from the garden hose with sprinklers running is not sufficient.(I would guess about 8 -10 GPM)
Obviously, I don't want to try it and damage the pump unless I know it would be safe.

 

[Valveman]

Won't hurt the pump as long as you have about 5 GPM going somewhere. Just don't put a nozzle that will close on the garden hoses and make sure at least 5 GPM is being let out somewhere when the pump is on.

 

[thegeeps20]

Won't hurt the pump as long as you have about 5 GPM going somewhere. Just don't put a nozzle that will close on the garden hoses and make sure at least 5 GPM is being let out somewhere when the pump is on.

thanks for the reply. Wow, just 5GPM. I thought it would be much more.
Edit: I'm in the process of ordering a new pump. New will have a 3" discharge and intake. My current pump set up with a 2" discharge has 1 foot length of 1 1/2 pipe directly from the discharge before going to the 3" pipe. Will going to a 3" discharge pump and keeping the same set up be detrimental in any way?

 

[MicEd69]

So, your question is if you install a pump with a 3" discharge to a 1-foot section of 1 1/2" pipe that immediately goes to 3", is that going to cause a problem. It won't cause a problem other than throttling the flow from the pump limiting the maximum flow rate you could get by installing a larger pump. In essence you have an orifice with 1.77 square inches of area before your flow enters a pipe with a 7 square inch area.

I think you might want to increase your line to 3" all the way to the pump.

 

[thegeeps20]

So, your question is if you install a pump with a 3" discharge to a 1-foot section of 1 1/2" pipe that immediately goes to 3", is that going to cause a problem. It won't cause a problem other than throttling the flow from the pump limiting the maximum flow rate you could get by installing a larger pump. In essence you have an orifice with 1.77 square inches of area before your flow enters a pipe with a 7 square inch area.

I think you might want to increase your line to 3" all the way to the pump.

Yeah, I should do it right. This is the mess I have now, lol. Would a 3" camlock fitting be suitable to plug directly into new pump's 3" discharge? I could simply get a 3" hose barb and extend the black 3" poly pipe right to a camlock and attach to male camlock at discharge.

 

[MicEd69]

Yes, that would work. You just need to be sure your final install doesn't put pressure on the pump fittings. Make sure you have a geometry that won't stress the pump when things start to move due to the black poly growing and shrinking due to temperature changes, sunlight, etc. I don't know if this goes underground quickly or if it lays on the ground and is subject to movement.

 

[thegeeps20]

Yes, that would work. You just need to be sure your final install doesn't put pressure on the pump fittings. Make sure you have a geometry that won't stress the pump when things start to move due to the black poly growing and shrinking due to temperature changes, sunlight, etc. I don't know if this goes underground quickly or if it lays on the ground and is subject to movement.

Would a piece of ABS pipe do the job here? Home depot sells 2" sections, but description states not for use under pressure, for drain, waste only. It's .23" thick, wouldn't that be plenty strong enough?...or would PVC be better? I'm not sure what my current 3" black pipe is, but it's been there about 30 years, some in the sun.

 

[MicEd69]

No, when your pump can develop around 90 psi, you cannot use a piece of pipe rated at atmospheric pressure. Whatever piping you use need to be rated at least at 150 psi.

 

[thegeeps20]

Here is the updated discharge. Little better than previous set up(look at pic upthread)
New pump has the exact same Honda 8HP (GX270) and the sprinkler heads are shooting water a good 10 feet further.
Question: Engine is using almost twice as much gas as previous pump to run the same amount of time. Previous pump ran at full throttle and I slightly throttle back new pump. A quart of gas on previous pump would last about 35 minutes, new pump, 20-22 minutes. Any good explanation for this?
Also, I want to confirm that I could run a few garden hoses at about 12-15GPM each and turn off sprinkler heads without damaging the pump? I feel that the sprinkler heads are throwing so much water that turning them off would create back pressure and would blow the camlock fitting off at the end attached to the pump.

edit: could I just throttle engine down to the point where I'm getting enough water from the garden hoses, but not
having a huge build up in pressure?

Here is the new pump: IPT Pumps 3P9XHR - 185 GPM 3-Inch High Pressure Water Pump w/ Honda GX270 Engine



e