PD Pump Deadhead Pressure

[Krausen]

All,
I'm accustomed to reading centrifugal pump curves that show the deadhead (shutoff head) head/pressure represented by the pressure in the discharge line at zero flow against a closed discharge valve. However, I'm having trouble with a PD gear pump application and potential discharge line overpressure. The gear pump itself is rated to 3000 psig but will only have a 5 HP motor operating on 240 V 1 phase power. The system will only need 300 psig maximum, but will typically be lower around 150 to 200 psig range. In the event of a blocked discharge line, I am thinking this 5 HP motor will shutdown from overload or trip a breaker before pressuring up to anywhere near 3000 psig. Can anyone advise on what the max discharge pressure of this gear pump & motor combo could be?

This may be more of an electrical question. What I do know is the circuit is protected by a 40 amp breaker and the full load amps (FLA) of motor while operating at 300 psig & 19 gpm is only 21 amps. I believe the in-rush (starting) current is ~120 amps.

Thanks in advance

 

[BigInch]

The pump is rated to 3000, but apparently only reaching 300 psig is actually necessary.

 

[lukin1977]

Just curious
What is your motor´s FLA read at nameplate? and for what voltage?

 

[Krausen]

hydtools - BigInch is correct. The pump is rated to 3000 psig, but only needs to discharge up to 300 psig at 19 gpm rate. That's why it's only a 5 HP motor.

lukin1977 - FLA = 21 amps. Voltage = 230 Single, 1 Phase, 60 Hz. RPM = 1745. Service Factor = 1.0. Full Load Torque = 15.1 ft-lbs. Start Config = Direct On Line. Breakdown Torque = 35 ft-lbs. Locked-Rotor Torque = 29 ft-lbs. Starting (in-rush) Current = 139 amps. NEMA Design Code = L

 

[Krausen]

LittleInch - Thanks for pointing out the 40 amp breaker issue. I confirmed with the Sparkies and they've since changed this circuit to a 30 amp breaker.

 

[LittleInch]

Whilst I still wouldn't recommend it, it would seem that your worst case locked rotor toque would generate around 600 psi on a non shock basis and would now probably trip on excess amps.

Given you normally run at less than 300 psi, I would set the trip setting on the breaker a bit closer to your max running current if this doesn't affect the max starting current ( 7 X FLC is high but not that bad so I would hope not).

not sure what you're going to do with this info now, but I wouldn't work on anything less than 1000 psi if you're going to work without a relief valve (bad idea IMHO) or set the relief at something a bit more reasonable like 400 so you don't get into a lock up / stall situation with your motor.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hydtools]

Krausen, so you are not drawing 21 amps at 19 gpm and 300 psi. That amperage is nameplate amperage. Your original post indicated you measured 21 amps with 19 gpm and 300 psi load.

Ted

 

[lukin1977]

"Can anyone advise on what the max discharge pressure of this gear pump & motor combo could be?"

If the motor is already drawing 21A at 300psi and if FLA (nameplate) is 21 A, then 300psi is the maximum pressure you can get before you start to overload the motor