fresh water pump vs. wash down pump?

[oak_box]

I'm probably going to need to replace my washdown pump. I have a spare fresh water pump (just in case the existing one dies - I don't want to be without water for days waiting for one to ship...).

Fundamentally, is there a difference between a "wash down" pump and a "fresh water" pump?

Both seem to pump about 3 GPM, both have pressure switches to turn them off when the output pressure hits between 40-70psi.

I don't see that either is better suited for salt water, or that either is better suited for being self-priming from a thru-hull that it might not be next to, or be able to pump a higher distance (though the higher PSI that I saw on one wash down pump might address that?).

Would you use the same type and model of pump for each application, or is there something specific to look for in each?

Thanks!
John

 

[tiltrider1]

In this day and age most fresh water pumps are variable speed pumps delivering a constant pressure at variable volumes. Wash down pumps are generally simpler with just an on or off pressure switch.

On my last boat I had one freshwater pump and two wash down pumps. I used the the same Sure variable speed pump for all three applications. This meant I always had a back up pump Incase of emergency.

 

[jgwinks]

Many of the wash down pump kits are a fresh water pump with a trigger nozzle included. A fresh water pump from the same manufacturer is the same pump without the nozzle. Don't know which pump the OP has but it's probably the same.

 

[rslifkin]

For the most part, they're interchangeable. That said, my washdown pump is much bigger than the fresh water pump. My fresh water pump is a Jabsco that's rated at 4 gpm open flow, 60 psi pressure switch.

My washdown pump is a Delavan FB2. Draws a lot of amps, but it's rated at 7 gpm and can handle being run at 100 PSI. With a nozzle installed, it pumps somewhere around 4.5 - 5 gpm and somewhere around 60 - 80 PSI. In other words, it's a stronger spray from the nozzle than most dock water supplies (although it can't move as much volume through an open hose with no nozzle).

 

[Mac2]

I am wondering if there is a difference in duty ratings? I just smoked my washdown pump, which is a pressure washer set-up. Sometimes it will take me up to 45 minutes to bring in my muddy anchor. A continuous duty motor will be a priority for me.

 

[jgwinks]

I am wondering if there is a difference in duty ratings? I just smoked my washdown pump, which is a pressure washer set-up. Sometimes it will take me up to 45 minutes to bring in my muddy anchor. A continuous duty motor will be a priority for me.

There are heavier duty versions of both pumps. Just most of the wash down kits use the same pump as their PW kit. You certainly could go with a heavier duty pump than the one you burned up, the duty cycle certainly is higher. It would be unlikely to run the PW pump 45 minutes continuously, you'd probably run out of water before that.

 

[Mac2]

There are heavier duty versions of both pumps. Just most of the wash down kits use the same pump as their PW kit. You certainly could go with a heavier duty pump than the one you burned up, the duty cycle certainly is higher. It would be unlikely to run the PW pump 45 minutes continuously, you'd probably run out of water before that.

My Pressure washer can be run with raw water, so no worries about running out of water. The wash down pumps I have looked at are not continuous duty rated, or they don't state how they are rated.

 

[tiltrider1]

There are all kinds of pumps out there. Amazon, Defender & WM tend to sell the cheap stuff. Every boat I have ever bought came with a cheap pump. Before long it gets replaced with a high end pump.

I like Marco pumps. I like the model 10 for volume and pressure. Pau Hanna likes the Mach5. There are a lot of options out there you just need to be willing to spend more money.

As time goes by there are fewer differences between wash down and fresh water pumps. The most common difference is variable speed versus non variable speed. Eventually it will be cheaper to just produce one model and then they will all be the same.

 

[Mac2]

There are all kinds of pumps out there. Amazon, Defender & WM tend to sell the cheap stuff. Every boat I have ever bought came with a cheap pump. Before long it gets replaced with a high end pump.

I like Marco pumps. I like the model 10 for volume and pressure. Pau Hanna likes the Mach5. There are a lot of options out there you just need to be willing to spend more money.

As time goes by there are fewer differences between wash down and fresh water pumps. The most common difference is variable speed versus non variable speed. Eventually it will be cheaper to just produce one model and then they will all be the same.

Thanks for the recommendation!

 

[rslifkin]

Many pumps give a max motor temperature and ideally provide a heat rise graph in the documentation.

For the Delavan FB2 I'm running as a washdown pump, max recommended motor temp is 180* F. They make a version with a heatsink on the motor for long runtimes in hot environments. However, looking at the heat rise graph for the non-heatsink version running at 100 PSI in a 72* environment, it'll never hit 180* meaning it's continuous duty under those conditions. Looks like motor temp reaches 110* after running for 30 minutes, just over 130* after an hour and just under 140* after 2 hours.

The Delavan pump does not have a thermal cutoff on the motor so if running it for long periods in a warm environment I'd consider the heatsink version with a fan pointed at it. I've never run mine for more than 10 - 15 minutes continuously, so I haven't worried about it.

The Jabsco pump (actually sold as a washdown pump, it's a Hotshot HD4) I'm running as a fresh water pump also has similar data available. It's officially rated as intermittent duty, but the heat rise chart shows it's unlikely to hit the thermal cutoff (at ~80* C motor case temperature) unless my engine room is rather warm and the pump runs for a long time. At 70* F ambient, the motor case will reach 50* C in 30 minutes, 60* C in an hour and about 66* C in 2 hours running at its 60 PSI maximum rating.

The bigger 6 GPM / 70 psi version of the Jabsco pump is definitely not continuous duty, however, as the heat rise chart indicates that while running at 70 PSI in a 70* F environment, the motor case will hit 70* C in 30 minutes and trip the thermal cutoff at about 36 minutes.

With any diaphragm pump like my examples above, running at lower pressure will reduce motor load and increase the duty cycle. Ambient temperature where the pump is installed will impact the duty cycle as well. The provided graphs are usually for the worst-case loading scenario of running continuously just shy of the pressure switch cut-off point.