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FS200 Adjustable Marine Grade Raw Water Flow Switch
Protect your engine from overheating!

Flow Set Point Range

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Throughout my 40 years of sailing I've experienced a variety of engine difficulties, as I'm sure you have, dear reader. My vote for the most common and possibly the most likely to cause damage is overheating. This is due to the many ways an overheating problem can occur. Here are the top five ways (add "while underway" to complete each sentence):
  1. I forgot to open the raw water seacock and I didn't check my exhaust for flow
  2. Strainer clogged
  3. Belt failure
  4. Impeller failure
  5. Pump bearing failure
There are a lot more reasons for overheating an engine but you get the general idea.

Here's the point: By the time your engine temperature sensor sends out an audible alarm (Assuming you have one and it works) it's already too late. She's cooking! What's for dinner? - Water hoses, a warped head and a belt "al dente".

Temperature damage in marine engines is well documented. I won't belabor the point but up until now there hasn't been an easy solution for monitoring the flow of incoming raw water.

We looked at units that sense water flow on the engine output but decided against it. We did not want to have to add any engine modifications. We also wanted a reliable test signal at startup and a continuous signal while the engine is running.

Bingo! We found it. The FS-200. It's rugged, reliable and simple to install. The FS-200 is a bronze N/C (normally closed) and N/O (normally open) switching device (SPDT) that does not impede the flow of raw water. It works equally well with salt and fresh water.

Adjustable switching set point: Each engine is a little different. The adjustable set point allows you to set the switch to activate at the exact flow that you need. The FS 200 will never inhibit flow regardless of the set point adjustment.

Unit Placement: The FS 200 is placed in-line between the raw water strainer and the raw water pump on your engine. The FS-200 is not connected to your engine in any way!

Easy to Install: You simply connect the N/O lead to your current engine alarm or install a new engine alarm. Connect the N/C lead to a dash panel light. I use a green 12VDC LED from Radio Shack®. The green light assures you that raw-water is flowing at a glance and gives you a cross-check for the alarm signal. Our instructions take you through the simple wiring required.

The FS 200 has a 1" inlet and outlet that adapts to all standard hose sizes. For example, a Yanmar 3GM30 uses a ½ inch bushing adapter and hose barbs. To adapt the FS 200 to your boat's raw water hose, just pick up the appropriate bronze bushings and hose barbs from your friendly local hardware store.

 Wetted Materials  
  -  Housing  Bronze 
  -  Shuttle  Teflon® 
  -  Bonnet  Bronze
  -  Spring  316 Stainless Steel 
  -  Other Wetted Parts  Viton® , Ceramic 
 Pressure Rating  
  -  Operating  400 PSIG @ 100°F (37.8°C) 
  -  Proof  800 PSIG @ 100°F (37.8°C) 
 Operating Temperature   -20°F to +200°F (-29°C to +93.3°C) 
 Repeatability   1% Maximum Deviation 
 Set Point Accuracy   ±10% 
 Set Point Differential   15% Maximum 
 Switch   SPDT, 20 VA 
 Electrical Termination   No. 18 AWG, 24˝ L., Polymeric Lead Wires 
#18 AWG., 24 " L., Polymeric Jacket
1/2 " NPT
Switch Housing
Inlet Port
6 NPT Port
A 3-1/4" (82.6 mm)
B 3" (76.2 mm)
C Hex 1-25/32" (45.2 mm)
The FS 200 fits in-line with the following engines in the 18 - 60 HP range including:
  • Yanmar
  • Westerbeke
  • Perkins
  • Volvo
  • Universal
  • Detroit Diesel
1-year manufacturer's warrantee.
Flow Estimator

You should check with your engine manufacturer for the an absolute recommendation for flow rate. We estimate 15 gpm / 100 bhp. Here's a calculator:

Engine HP:    Flow= gpm.
Instruction Manual: DOWNLOAD
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