[modeleng] Fw: Re: Lapping, pumps, etc was
- From: "Jesse Livingston" <fernj1@xxxxxxxxxxxxx>
- To: <modeleng@xxxxxxxxxxxxx>
- Date: Mon, 20 Feb 2006 08:49:26 -0600
> 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.
>>
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>>
>
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