Sea Strainer Alarm - what triggers alarm?

[srah1953]

In a review of engine exhaust alarms in March 2011, PBO reviewed the Halyard Sea Strainer Alarm. This, it is stated, works by sensing a reduction in pressure in the pipe that would be caused by a blockage. The review goes on to say that the strainer would not be sufficient protection in itself as it won't monitor a failed water pump impeller. Surely, if the impeller failed, the water will stop flowing- would this not change the flow through the strainer alarm and trigger the alarm?

 

[sailorman]

i have a piddler in the cockpit ( between raw water pump & HE) & it doesnt use any electricity at all

 

[pvb]

In a review of engine exhaust alarms in March 2011, PBO reviewed the Halyard Sea Strainer Alarm. This, it is stated, works by sensing a reduction in pressure in the pipe that would be caused by a blockage. The review goes on to say that the strainer would not be sufficient protection in itself as it won't monitor a failed water pump impeller. Surely, if the impeller failed, the water will stop flowing- would this not change the flow through the strainer alarm and trigger the alarm?

The Halyard info isn't specific, but it does concentrate on "water flow", so I'd agree with you that a seriously failed impellor should also result in an alarm. But, as ever, don't take anything you read in a magazine "test report" as gospel!

 

[prv]

But, as ever, don't take anything you read in a magazine "test report" as gospel!

+1

Pete

 

[JSYmartini]

I've got Halyard strainer alarms fitted. Had a blockage on one engine last season, noticed the temp gauge climbing, looked over the transom and there was nothing more than a dribble. At no point did my alarm go off and I wasn't going to leave it to see if it would.

Fat lot of good that was. I always check over the back every time I fire up but on this occasion I was drifting about a lot with the engines idling as I was guard boating a rowing race so I got caught out.

 

[srah1953]

I've got Halyard strainer alarms fitted. Had a blockage on one engine last season, noticed the temp gauge climbing, looked over the transom and there was nothing more than a dribble. At no point did my alarm go off and I wasn't going to leave it to see if it would.

Fat lot of good that was. I always check over the back every time I fire up but on this occasion I was drifting about a lot with the engines idling as I was guard boating a rowing race so I got caught out.

Had you ever tested it prior to this by gradually closing off the seacock to see if the alarm sounded?

 

[JSYmartini]

Had you ever tested it prior to this by gradually closing off the seacock to see if the alarm sounded?

You've got me thinking now, I may have to retract my last and blame myself instead

There's an "accessories" switch on the console, it powers up the raw water and exhaust alarms, not sure if anything else runs off it.

Not having the boat all that long, I think I may have quickly fallen out of the habit of flicking this switch on which would obviously explain a lot

Next time I run the engine I will do a quick test on how sensitive it is. It does also bleep when you turn it on, I'm assuming this is some sort of self test but the instructions don't tell you much.

I'm guessing the alarm is wired so it knows when the engine is running, otherwise it would bleeping away whenever the engine is stopped and no water is flowing?

 

[nimbusgb]

If the alarm works on pressure then a failed pump will not give an alarm on the strainer.

If the strainer is blocked the pressure in the pipe between the strainer and the pump will drop well below atmospheric, thus triggering the alarm.

A failed pump will not reduce pressure and will not set off the alarm.

A flow ( rate ) sensor is a much better idea, backed up by an exhaust temperature sensor.

 

[Rivers & creeks]

i have a piddler in the cockpit & it doesnt use any electricity at all

I have a doggie on board as well but I've house trained him. Recommend some newspaper and regular walks ashore.

 

[sailorman]

I have a doggie on board as well but I've house trained him. Recommend some newspaper and regular walks ashore.

Ah but this way i can see in a trice if the raw water has a blockage. The water stops & an audible, gurgling sound is noticeable.
Anyways doggies have to be taken ashore every day for No 2s

 

[srah1953]

If the alarm works on pressure then a failed pump will not give an alarm on the strainer.

If the strainer is blocked the pressure in the pipe between the strainer and the pump will drop well below atmospheric, thus triggering the alarm.

A failed pump will not reduce pressure and will not set off the alarm.

A flow ( rate ) sensor is a much better idea, backed up by an exhaust temperature sensor.

In the operating instructions, all it says is that the “sea strainer monitors the flow of water to the engine”. It doesn't say what exactly triggers the alarm.

 

[coopec]

In the operating instructions, all it says is that the “sea strainer monitors the flow of water to the engine”. It doesn't say what exactly triggers the alarm.

I am quite sure Nimbusq is correct - it would work on pressure within the intake pipe before the raw water pump. Since atmospheric pressure at sea level is 14.4 lb/ft 2 they probably set the alarm to go off if the pressure falls below 10 lb/ft 2. If it falls below that there MUST be a restriction so it sets the alarm of. (They would have a pressure sensor to trigger the alarm)

 

[cryan]

filter/strainer alarms are usually set on pressure differential across the unit. In the old days they used to just fit a U-tube manometer for visual indication.