# Pressure Drop



## Plumberman (Jul 7, 2008)

I am currently on site of a massive drill ship renovation. We are adding another galley, 12 man sleeper, 2 4 man sleepers, 2 bathrooms and wash rooms. 

I will have to run a potable water feed cold&hot from below deck from their pump room. I haven't calculated the entire developed length of the pipeline (tomorrow project). For the sheer volume needed I am going to be running 2" pipe to our new add on (cold and hot)

The original plan was to install a Eemaxx EX-144TC instantaneous water heater above a commercial dishwasher. When I received the specks for the dishwasher and its minimum psi requirement, red flags went off.

I have installed a few emaxx heaters and they are designed as a whole house heater for on demand hot water. Not designed for the application here. 

The min psi to run the dishwasher is 20-22 psi.

They are able to supply 50-55 psi from the pump room.

Am I safe to assume at least a 30-40 psi drop through the heater to the dishwasher which would put me at too low of a pressure to operate it at its minimum requirement?

I do understand the physics behind water volume over psi, but it's not a GPM flow rate I have to be at.

The few emaxx I've installed have drastically cut the flow rate down, enough where I had to install boosters on the outlet side to achieve the required psi...


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## Nathan901 (Feb 11, 2012)

Step one, don't use emaxx haha.


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## ironandfire (Oct 9, 2008)

Is that the only option you have ?


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## Plumberman (Jul 7, 2008)

ironandfire said:


> Is that the only option you have ?



No my rough sketch plan right now is to run a 2" feed and carry a return line with it.

We are more than likely re doing the pump room as well which will allow me to install a pumped dedicated return for our addition.


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## Plumberman (Jul 7, 2008)

Thanks for the help mates!


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## Plumberman (Jul 7, 2008)

Nathan901 said:


> Step one, don't use emaxx haha.


I wasn't the one to survey the job, if I would have been it wouldn't have eve been ordered


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## ironandfire (Oct 9, 2008)

Where's the booster heater for the DW ?


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## Nathan901 (Feb 11, 2012)

Most washers have do have boosters. The issue really is pressure. You want the machine to actually clean the dishes. Even if the machine says it will operate on 25 psi, it probably won't do a very good job. 


The only tankless I would ever install to service all of that would obviously be a gas unit , which I'm sure isn't feasible. I'd be willing to bet a pump on the outgoing side of a cheap heater would burn it up in no time 

Is a tank completely out of the question? I'd be guessing you would be installing more than one emaxx? Id be worried if there is enough space in your panels for all that amperage. 

I've been through that scenario on a large boat where we installed a bunch of point of use heaters. 

What type of existing water piping are you working with?


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## Redwood (Sep 8, 2008)

How far above the pump are you?
What is the performance curve of the pump with that discharge head pressure?

Can you get what you need?


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## Plumberman (Jul 7, 2008)

The dishwasher does have a heat booster, it didn't specify if it boosted pressure as well. I just know I will be under the psi rated delivery if it went through the emaxx.

The pressure set and heaters are going to be replaced during this renovation/addition. It is on the 2nd deck of a 4 deck ship and will be serving the entire vessel. 

I'm planning on having a dedicated return just for the addition. I'm thinking the return that goes up and down the vessel is going to cause problems if put back into service.

The piping on the outside is going to be welded steel. The interior piping will be SeaCor (low flammability sch 80 PVC)


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## PathMaker (May 10, 2013)

Some commercial dishwashers are just metal boxes that heat the water in the bottom pan and fling it really hard upward at the dishes to clean them. The incoming PSI would, in many cases only affect the time it takes to fill the box, and not directly squirt the dishes. Of course, I cant see the specs for your DW from here, but it would be worth checking out.
I would imagine that if this particular machine DID need pressure to squirt the dirty dishes directly, the specs would require a much higher minimum PSI than 20-25... just my .02


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