For centrifugal pumps (the most common kind) that's true, they only run one way. But there are pumps that can run in either direction with the same efficiency. Problem is, from what I've see so far their efficiency is very low. Using Cliff's formula, it looks like they would not provide enough thrust. Alec ________________________________ From: owner-personal_submersibles@psubs.org on behalf of vbra676539@aol.com Sent: Thu 1/4/2007 2:12 PM To: personal_submersibles@psubs.org Subject: Re: [PSUBS-MAILIST] Thrust from a pump? Pumps do run in one direction, right? Running one backwards is inefficient. Change the flow downstream. Vance -----Original Message----- From: nomdae@hotmail.com To: personal_submersibles@psubs.org Sent: Thu, 4 Jan 2007 2:07 PM Subject: RE: [PSUBS-MAILIST] Thrust from a pump? I had to replace the motor on my pool pump last summer. Six bolts held the motor against the pump housing. To disconnect the impeller, I simply put a screwdriver into the motor to prevent it from turning and unscrewed the impeller off of the motor shaft with my hands. My concern is that some pool pumps are designed to run in only one direction, and that reversing one would either not work at all, or could make it fall apart. -- NP ________________________________ From: "Smyth, Alec" <Alec.Smyth@compuware.com> Reply-To: personal_submersibles@psubs.org To: <personal_submersibles@psubs.org> Subject: RE: [PSUBS-MAILIST] Thrust from a pump? Date: Thu, 4 Jan 2007 11:50:42 -0500 >Yes, and in addition depending on the type of pump a thrust bearing >could be on the wrong end of the shaft in "reverse". > >Lots of food for thought here... > >Alec > >-----Original Message----- >From: owner-personal_submersibles@psubs.org >[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Dan H. >Sent: Thursday, January 04, 2007 9:45 AM >To: personal_submersibles@psubs.org >Subject: Re: [PSUBS-MAILIST] Thrust from a pump? > >But Alec, >Wouldn't using a reversible pump as a thruster require you to use two >small output nozzles instead of a larger suction input and ported down >output nozzle. I'm not sure if the pump would like that. Sounds like a >cavation problem. > >Maybe a single direction pump and a Y valve to two separate output >nozzles????? > >Dan H. >----- Original Message ----- >From: "Smyth, Alec" <Alec.Smyth@compuware.com> >To: <personal_submersibles@psubs.org> >Sent: Thursday, January 04, 2007 9:16 AM >Subject: RE: [PSUBS-MAILIST] Thrust from a pump? > > >Wow, what an A+ response! Thanks Brian for yours as well. With this >information I can now go out and do some virtual shopping to see how >much >I'd have to spend to accomplish the same thrust with the two approaches. >Off >hand I'd say the well pump solution would likely be cheaper, but mating >trolling motors to pump heads makes use of two brand new trolling motors >I >happen to have sitting in the garage. > >thanks, > >Alec > >________________________________ > >From: owner-personal_submersibles@psubs.org on behalf of Cliff Redus >Sent: Wed 1/3/2007 8:58 PM >To: personal_submersibles@psubs.org >Subject: Re: [PSUBS-MAILIST] Thrust from a pump? > > > >Alec, > > > >Below is a derivation of thrust that can be developed from a axial flow >pump >in terms of volumetric flowrate. > > > >The thrust due to accelerating fluid through a pump can be written as > > > >F=M(V1-V0) > > > >Where M is the mass flow rate, V0 is the free stream velocity upstream >of >the pump and V1 is the velocity exiting the pump. > > > >But the mass flow rate M can be related to the volumetric flow rate Q as > > > >M=Density*Q > > > >Substituting, the thrust in terms of volumetric flow rate is > > > >F=Density*Q(V1-V0) > > > >But the volumetric flow rate Q is related to velocity in the pump duct >ID as > > > >Q=V1*A=V1*Pi*D^2/4 > > > >Where D is the duct ID. > > > >Solving for V1, and substituting, the thrust can be written as > > > >F=Density*Q(Q/(Pi*D^2)-V0) > > > >For a thruster oriented approximately normal to the direction of flow, >the >inlet velocity can be assumed to be zero. The thrust then reduces to > > > >F = 4*Density*Q^2/(Pi*D^2) > > > >Or > > > >F= 0.001766*(q/d)^2 > > > >for freshwater where, > > > >F = Thrust, lbf > >q = pump volumetric flow rate in gpm > >d = pump outlet duct inside diameter in inches > > > >As an example, a pump with a capacity of 200 gpm flowing through a 2" >duct >would develop 17.7 lbf of thrust. > >Cliff > > >----- Original Message ---- >From: "Smyth, Alec" <Alec.Smyth@compuware.com> >To: personal_submersibles@psubs.org >Sent: Wednesday, January 3, 2007 4:20:48 PM >Subject: [PSUBS-MAILIST] Thrust from a pump? > > > >I'm contemplating using water pumps as maneuvering thrusters (NOT for >main >propulsion). Cousteau's socoupe used a hydraulic pump for the jets, but >I'd >like to avoid that route if possible due to the excessive noise. DC >submersible pumps are convenient but I haven't found anything beefy. I >could >try mating a trolling motor to a pump head. Submersible well pumps look >promising because they're very powerful yet compact, but they require >AC, >and I don't think I can reverse them so I'd need four pumps instead of >two. >I could of course hang trolling motors off the boat font and back, but >it >really messes up the hydrodynamics of what can otherwise be a quite >clean >design, and the props on my trolling motors make them too large to duct >into >the MBTs. > >Assuming I do settle on some kind of pump, the next question is how >strong >it needs to be. Does anyone know how to translate GPM (or LPM) into >static >thrust? > >Any ideas or experiences would be much appreciated. > > >Thanks, > >Alec > >The contents of this e-mail are intended for the named addressee only. >It >contains information that may be confidential. Unless you are the named >addressee or an authorized designee, you may not copy or use it, or >disclose >it to anyone else. 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