Watermaker-Rainman

[bradm85]

A couple of summers ago I purchased a Rainman gasoline watermaker. The entire season I had issues keeping the engine running and had to continually adjust the choke in order to keep it running. Since the prime mover on this unit was a Honda engine which I had always found reliable I assumed I had a defective carb. Since the carb was only about $40 I decided to replace it, but still experienced the same problem. I contacted the manufacturer and they stated that this was standard operation with this unit. Well pardon me but IMHO if you have to continually adjust the choke to keep it running the issue is that the prime mover is underpowered for the job it is being tasked for. To me, it is obvious that they picked an undersized engine in order to keep the weight and size down to make it more attractive to market to the boating market. I really wished I had bought the 120v model that I could run with my generator. Is my reasoning faulty. Thanks for your input.

[Pegu Club]

We have the same Rainman unit, it runs well, we did get a new carb because we got water into our one gallon gas can, which of course ended up in our Rainman but that was our fault, we did find the Rainman customer service guy in Florida lacking in actual customer service, we emailed the home office about the complete lack of response to our carb issues, the home office responded within a day and were helpful in diagnosing our issue, We ended up purchasing the carb and had it shipped to the Bahamas where we are currently, the unit now starts right up and runs fine. Hope you get your issue resolved soon.

Fair winds,

[Pegu Club]

Another thought that might be the cause, are you using ethanol fuel ? We have had issues with small outboard engines not being happy with ethanol fuel, similar symptoms that you have described, even when living in ethanol states we started buying “true fuel” for all our gas engines outboard and Rainman, the issues went away, do check to see if you had water intrusion on the Rainman, that would as well cause those symptoms, best of luck to you.

Fair winds,

[rslifkin]

The ethanol thought is a good one. Most of my small engines run the same on E10 gas or E0, but my newer Honda mower seems to be jetted a little on the lean side to start with. E10 needs a bit more fuel than E0 to run perfectly. So on E10, the mower doesn't run quite as well under load sometimes seems a hair weak. As if it's running too lean. As a result, I do my best to keep that one fed with E0.

[Northbound44]

In regards to the engine size, an internal combustion engine may develop high enough torque to drive a loaded pump, but not enough to accelerate it to operating speed. Consequently, with all other factors being equal, a power unit requiring an electric motor of a given power rating usually requires a gasoline engine with a power rating more than double that of the electric motor.

In this case ( engine powered Rainman Watermaker), the AR plunger pump WM 2315C need a minimum of 1,26 HP ( EBHP= 2.3 GPMx800 RPM / 1457) without taking into account the energy losses caused by the belt friction as well as the energy required by the primary pump.

The motor used with this equipment is a Honda GXH 50, who can provide a maximum of 2.1 HP @ 7000 rpm (4:1 pulley ratio) which barely represents the minimum power required.

The Honda owner manual also give a warning concerning gasoline containing ethanol and mention that if you notice any undesirable operating symptoms, switch to another brand of gasoline .
Ref p.45 https://www.rainmandesal.com/wp-cont...h50-manual.pdf.

[dougweibel]

Originally Posted by Northbound44

In regards to the engine size, an internal combustion engine may develop high enough torque to drive a loaded pump, but not enough to accelerate it to operating speed. Consequently, with all other factors being equal, a power unit requiring an electric motor of a given power rating usually requires a gasoline engine with a power rating more than double that of the electric motor.

In this case ( engine powered Rainman Watermaker), the AR plunger pump WM 2315C need a minimum of 1,26 HP ( EBHP= 2.3 GPMx800 RPM / 1457) without taking into account the energy losses caused by the belt friction as well as the energy required by the primary pump.

The motor used with this equipment is a Honda GXH 50, who can provide a maximum of 2.1 HP @ 7000 rpm (4:1 pulley ratio) which barely represents the minimum power required.

The Honda owner manual also give a warning concerning gasoline containing ethanol and mention that if you notice any undesirable operating symptoms, switch to another brand of gasoline .
Ref p.45 https://www.rainmandesal.com/wp-cont...h50-manual.pdf.

I am not familiar with the acceleration load factor, though it seems reasonable and I believe you. However, a conclusion that the engine is undersized seems like faulty logic w.r.t. the OPs problem. The OP says he has trouble keeping the engine running. If the power demand of the pump drops off after it gets the pump up to operating speed then if the engine is capable of doing that it should have adequate power to continue operating the pump indefinitely.

[Pegu Club]

The engine is not undersized, as we are using the same Rainman model brought up in this thread, and have had no issue with it driving the pressure pump, we were happily making water at an eighteen GPH rate yesterday (using the compact size membranes) while anchored at Staniel cay, The OP did say he is having carburetor issues, ie; the choke not working as desired, which is likely caused by ethanol laced gasoline or water ingress to the gasoline being used, as his description of its performance seem to indicate. If it is not one of those two things causing the problem the OP should likely make arraignments to have the unit service by a Rainman, hopefully under warranty, fingers crossed �� . Just an opinion by a cruiser using the same model water maker. Hopefully the OP will come back with a response to our responses.

Fair winds,

[coriobay]

Sounds to me your main jet is blocked, strip the carby and use compressede air to clean all the jets, check the main jet is actually tight and correctly positioned.

[Davo1404]

We have the petrol driven unit with the compact membranes. Fantastic unit. Been using it for 2 years now, the little Honda never misses a beat.