The Eagle EP67 progressiving cavity pump is like a Robben-Myers Moyno; the unsupported stator is elastomeric. Thus, in my opinion, it isn't 'truly' a PD pump, like a Viking, Waukeshau, or Liquiflo, i.e. it does NOT have a flat pump curve or nearly vertical curve of flow vs discharge pressure at a given speed over its typical operating pressure range. Flow curve for this pump (EP67) shows about a 2:1 turndown of flow rate vs pressure in the 0-50 psi operating range, at a given rotational speed. This is due to the large amount of slippage that occurs between the Viton or BUNA stator and the rigid stainless or chromed steel screw as discharge pressure increases. This design is spectacular for slurries; the flexible stator allows passage of big chunks without damaging the rotor. The downside is slip, slip, and more slippage as discharge pressure increases -- and thus reduced flow -- because there is nothing behind the stator. Also the stators, have to be replaced when the rubber wears or ruptures, but stators are cheap. They're more frequently used for centrifuge slurry feed, mud, toothpaste, etc than for clean water in my experience. The flexible rotor with no support means it has a true 'curve' similar to a centrifugal pump, and that it has a low ultimate discharge pressure, unlike a traditional/conventional piston PD pump with a flat curve, or a metal-metal gear pump.
I would also double check that it is the EP67 model as you indicated in your e-mail; other progressing cavity models, provide a stator that is formed to a rigid stainless steel cylinder (old Moyno design); that type of stator will lead to a flatter pump curve akin to a traditional PD pump due to reduced slippage; however EP67 will have the 'soft' stator. The other style of stator with the SS cylindrical backing, has the advantage that it won't collapse under vacuum but is more expensive than the flexible stator. That style is more of a 'traditional' PD pump with a flat pump curve & thus unsuitable for reasons Art outlined.
The biggest issue I've had with these inexpensive pumps is when suction is blanked off; that tends to collapse the rubber stator requiring dismantling & thus should be avoided. The progressing cavity style also doesn't pulse whereas a plunger pump does. Parts are VERY inexpensive. Main downside is it isn't as good for metering if downstream pressure varies since flow rate will change & with their typical elastomeric stator, they can't attain very high discharge pressures. The rigid SS backed stator style can attain a couple hunded psi in the longer barrel design with more stages, but not thousands of psi. Also you have to be VERY careful with chemical compatibility; the stator is huge; any solvent that swells the Viton or BUNA stator, will cause the pump to bind requiring dismantling & stator replacement, I've seen this firsthand. Some vendors offer a teflon stator bound to a SS cylinder backing it. For your water application compatibility won't be an issue.
I don't have enough information to answer the sync question without knowing whether they're both on variable frequency drives, whether there is a relief valve/bypass, etc. I wouldn't deadhead the Eagle for long periods of time as it may overheat, same as a centrifugal pump. The rubber stator and seal might then fail. So if they aren't on frequency drives a relief valve back to feed tank may be adviseable, and/or a temperature safety to shutoff the eagle near the 50# max pressure. The unsupported stator style progressing cavity pump will not burst any pipes if it's deadheaded because of the extreme slippage, but it likely will still overheat without a slipstream recirc or relief valve back to feed tank.
Edited by fseipel, 27 July 2013 - 09:51 PM.
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