[modeleng] Fwd: Re: Re: Lapping, pumps, etc was

From: Allen Messer <al_messer@xxxxxxxxx>
To: modeleng <modeleng@xxxxxxxxxxxxx>
Date: Mon, 20 Feb 2006 06:08:53 -0800 (PST)

--- Phill Smith <steam@xxxxxxxxxxxxxx> wrote:

>> Subject: Re: [modeleng] Re: Lapping, pumps, etc was

> Date: Mon, 20 Feb 2006 13:25:25 +0800
> 
> Gents,
> 
> Modern fluid flow analysis has shown that the close
> fitting plunger in a
> bore causes more problems than it's worth, at other
> than low piston speeds.
> Optimal piston speed is below our "normal running
> speed" of our models. The
> greatest efficiency was found to be with a plunger
> operating in a free water
> space of at least twice the displaced volume of the
> plunger. The factors
> against the fitted plunger was due to the following
> factors;
> 
> - Insufficient valve area due to limited space. To
> over come this, the
> valves had to have a high lift. This in turn
> resulted in water being pumped
> back down the suction pipe (and/or into cylinder
> from the discharge valve)
> for up to 30% of the compression stroke (this was
> worst on unsprung ball
> valves). Vapour pressures were entered into in the
> worst cases (suction
> pressures dropped low enough for the water to
> momentarily turn to steam).
> 
> - Surge forces, due to rapid water flow in full
> cylinder, causing high
> friction losses and extenuating valve opening time.
> 
> 
> So, summing it all up.........
> 
> You'd have a 1/2" plunger operating in a minimum
> 3/4" bore, with the "O"ring
> gland mounted as close to the water space as
> practical within the gland.
> This can be a screw in (replaceable)
> gland/guide/support. The guide is made
> from an extension of the gland which is fed with
> oil. Two small grooves are
> placed, longitudinally, on the bearing area of the
> plunger carry oil. One
> top and bottom. The large cylinder will accommodate
> larger valves
> (preferably of the disc type), on the end if
> possible (with flow axis in
> line with the plunger) with an area equal to the
> plunger diameter.
> 
> This type of pump also allows for 2 different
> materials to be used for the
> plunger, and hence compatible bearing materials may
> be used for the gland
> and bearing area of the plunger. Especially since
> oil can be used as the
> lubricant.
> 
> 
> Cheers,
> 
> Phill.
> 
> PS     Could someone please post this to the
> "modeleng" discussion group, as
> I have not yet had time to sort out my "why I can't
> post anything (after a
> certain date) but receive fine" problem.
> 
> ----- Original Message ----- 
> From: "alan stepney" <alan@xxxxxxxxxxxxxxxx>
> To: <modeleng@xxxxxxxxxxxxx>
> Sent: Monday, February 20, 2006 8:07 AM
> Subject: [modeleng] Re: Lapping, pumps, etc was
> 
> 
> > I have used stainless, and a reamed bore, and not
> had any problems so far.
> >
> > I leave a reasonable clearance between the bore
> and ram so that the
> packing
> > is the only thing making contact.
> > That should (??) prevent galling.
> >
> > A reamed bore seems to be sufficiently smooth to
> work OK and wear well.
> >
> > Alan
> >
> > MODEL ENGINEERING DISCUSSION LIST.
> >
> > To UNSUBSCRIBE from this list, send a blank email
> to,
> > modeleng-request@xxxxxxxxxxxxx with the word
> "unsubscribe" in the subject
> line.
> >
> >
> 
> 


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[modeleng] Fwd: Re: Re: Lapping, pumps, etc was

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