Rotary pump conversion - balanced bypass or standard bypass model?

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coffee_monkey

#1: Post by coffee_monkey »

Hey you rotary pump experts,

Got some question re: pump spec for espresso use. I am trying to find a cheap unit on ebay to use w/ a home machine (Isomac Rituale). I know the GPH requirement is very low (just about every model Procon offers will do), but what about the bypass option. Based on my search, a "balanced bypass" option seemed to be preferred/required as it gives a fix output pressure regardless of input pressure fluctuation. Is this correct? Will the "standard bypass" model work? How about no-bypass models? Could something(valves/regulator/etc) be added to that to make it work?

Thanks!!


Ben

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erics
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#2: Post by erics »

I would rather quickly strike-out the "no-bypass" option. Even if you did mount a pressure regulator on the discharge side of the pump, you would be building up some rather high pressures on the pump side of the regulator. The nominal flowrate of the smallest Procon pump is over 4 times the flowrate of a typical double shot so it's easy to see that a high percentage of the pump's flow is simply being bypassed from the outlet back to the inlet (when the pump is so equipped).

As far as a balanced by-pass vice a standard by-pass, I would guess that most espresso machine installations have pumps with the standard by-pass valve but have their inlet pressure regulated down to 25-35 psi from standard water mains pressure (60-80 psi). You might want to measure your water main pressure at various times of the day or see what it falls to when your daughter takes that 30 minute shower or whatever. Call Procon and Fluid-O-Tech and ask how well their balanced by-pass valves work as compared to a high quality pressure regulator on the inlet side of the pump.

I would suspect that the least expensive route would be with a balanced by-pass valve but that might also be a "hard to find" pump on ebay.

Another option would be to remote mount your existing vibration pump like Dan did if you are bothered by the noise.

Eric S.

Cerini Coffee & Gifts: official US importer for Olympia Express
Sponsored by Cerini Coffee & Gifts
coffee_monkey (original poster)

#3: Post by coffee_monkey (original poster) »

Thanks Eric! I ultimately found out that ordering direct from Fluid-o-Tech is the cheapest and fastest method. I will get the balanced by-pass model and put a pressure regulator in front of the pump inlet. The pump will be remotely mounted.

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erics
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#4: Post by erics »

Hi Coffee Monkey -

Sorry I didn't make myself so clear. If you have a "quality" pressure regulator on the inlet side of the pump, you would NOT normally need a balanced by-pass valve built into the pump. In that case, a standard by-pass should suffice unless, perhaps, your mains pressure varied to such an extent and frequency that the inlet pressure regulator was beyond its capabilities.

If the rotary pump has a balanced by-pass valve, this is supposed to take care of varying mains pressure but I would wonder just how well they actually work under, lets say, difficult scenarios. Did any of the pump guys say anything in this regard?

I would also assume that the path you are taking is the "best" of all - i.e. two devices to guard against line pressure fluctuations and remote mounting. Did Fluid-O-Tech have any related comments and are you buying the pump & motor from them as a package?

Eric S.

coffee_monkey (original poster)

#5: Post by coffee_monkey (original poster) »

Actually you are perfectly clear, and I am just taking a very conservative approach (and that I already own a small pressure regulator from my direct connect kit). The balanced bypass option does not cost any more than a regular model.

A interesting conversation with them about using a higher flow rate model for my use. Basically, according to the engineer, if my flow rate requirement is low and a high flow rate model is use (say, 100 GPH), there is a chance for excessive backpressure build-up if I don't get the bypass model. And even if I do, if the flow differential is too high, the bypass valve will wear out much faster due to the higher duty impose on it (and he really do not like how "we" use the bypass pump as pressure regulation, but I explain it's for intermittent duty only). So, I am getting the smallest model they offer.

I got a brand new emerson 1/4 hp motor from ebay for $25 -> can't beat that!

HAL9000

#6: Post by HAL9000 »

erics wrote:I would rather quickly strike-out the "no-bypass" option. Even if you did mount a pressure regulator on the discharge side of the pump, you would be building up some rather high pressures on the pump side of the regulator. The nominal flowrate of the smallest Procon pump is over 4 times the flowrate of a typical double shot so it's easy to see that a high percentage of the pump's flow is simply being bypassed from the outlet back to the inlet (when the pump is so equipped).
Hi Eric,

I have been looking into these pumps recently and have been under the impression that the "relief" valve allows flow from discharge side to input side to regulate pressure, but that the "bypass" (if so equipped) allows flow from input to discharge when the pump is not operating. Is this incorrect?

Thanks!
Paul

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erics
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#7: Post by erics »

Hi HAL9000,

Firstly, your statements are correct.

The "relief" valve on the pumps typically used in the beverage industry (that's us) is of the by-pass type in that a certain amount of flow (certainly enough for pre-infusion) is allowed to pass from the inlet side of the pump to the discharge side of the pump when the pump is NOT OPERATING.

The "relief" valve can be a "balanced" type such that it will regulate to a certain (factory set/user adjustable) pressure regardless of what the inlet pressure is (flushing toilets, taking showers, etc., etc.).

The "relief" valve can be a "standard" type such that it will regulate to a certain (factory set/user adjustable) differential pressure between inlet and outlet. If one were to set the relief valve to 150 psi with 50 psi inlet pressure, it would rise to 175 psi with 75 psi inlet pressure. This would likely not be the case with a "quality" pressure regulating valve installed in the supply line to the pump because then the inlet pressure would be reasonably constant regardless of events (flushing toilets, taking showers, etc., etc.).

But the best of all possible worlds, especially at no $ differential, as Coffee_Monkey pointed out, is to spec a pump out with a balanced bypass relief valve.

Eric S.

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HAL9000

#8: Post by HAL9000 »

Thanks Eric, makes sense to me.

Paul

coffee_monkey (original poster)

#9: Post by coffee_monkey (original poster) »

erics wrote: If the rotary pump has a balanced by-pass valve, this is supposed to take care of varying mains pressure but I would wonder just how well they actually work under, lets say, difficult scenarios. Did any of the pump guys say anything in this regard?
I ended up not using a pressure regulator after all. The one I had (that came w/ Chris' direct connect kit) developed a leak as I over-torqued a pressure gauge on one of the plastic port. Didn't felt like spending another ~$40 on one, so I decided to let the pump take care of itself.

The engineer at Fluid-o-Tech told me that the pressure regulation is good for up to a pressure differential of 250 psi - nothing to worry about in our application. The pump, directly from Fluid-o-Tech, costed me only $66 (or is it $62, not sure) and took a whopping one day to ship. I would highly recommand buying directly from them if anyone is looking into getting a unit.

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erics
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#10: Post by erics »

Personally I believe that's stretching it a bit but I certainly have no factual data or experience with espresso machine rotary pumps. I have, however, seen my fair share of pumps of all types, including rotary vane.

Why not give it the acid test? Pull a good shot at "X" bar brew pressure in your normal manner. Now go open up some/all of the faucets in the house which will cause your house mains pressure to drop by about 1/3. e.g., from 75 to 50 or from 60 to 40. Now pull another shot - do you still get "X" bar brew pressure?

Eric S.