Each of the systems you are running together require a healthy source of raw water to run. At the end of the season we run fresh water through all systems. We run each system individually so we can keep up with water demand. We accomplish this by shutting off the main sea water valve, removing the sea chest cover and using a 3/4 inch hose to supply the fresh water. We can run all systems individually with just one 3/4 inch hose at full flow. However, the Volvo running at idle requires more water than the single hose can provide. Therefore we use two hoses and by reducing one down to half flow, we can keep a constant water level in the sea chest.
The point being that the Volvo at 1250 RPMs (much more water requirement than at idle), the A/C and water maker running together will require a large flow of raw water. I would start by looking at anything that could restrict this flow. From the raw water valve not opening completely when you turn the valve, a rubber supply hose failure on the inside, a kink in the line, etc. I would also try shutting off the main sea water chest valve, remove the raw water supply to the LP Dessalator pump and turn on the sea water valve to see what kind of flow you are getting to the LP pump.
Mohammad and Aty
Amel 54 #099
From: amelyachtowners@... [mailto:amelyachtowners@...]
Sent: Tuesday, April 10, 2018 7:17 PM
Subject: [Amel Yacht Owners] Dessalator Operational Question
We have an A54 with a 230v 160 LPH Dessalator, water cooled air conditioning, and a Volvo 110 HP engine.
1) When operating the Onan, water maker, and the Volvo above approximately 1250 RPM the low-pressure gauge on the water maker drops from 20 psi to negative 10” hg, the high-pressure pump starves, and the water maker shuts down.
2) When operating the Onan & water maker everything operates correctly IF the air-conditioning is started first. If the water maker is started before the air conditioner when the water maker is started the low-pressure pump pressure drops and the water maker shuts down due to low-output pressure on the high-pressure pump.
All tests were run with a clean sea strainer and a clean raw water intake pipe, it was scrubbed with a round brush that reaches through the hull.
What has been your experience? Any
thoughts? Thanks in advance.
Mark & Debbie Mueller
A54 – 68