Vetus waterlock muffler size for Volvo MD2020

[Ric]

The original Volvo Penta waterlock muffler on my MD2020 has developed a pinhole leak.

I am looking at buying a Vetus plastic replacement - much cheaper and more durable too. But how do I calculate the size required?

The Vetus mufflers seem to be available in either 4.7litres or 10.5 litres but nothing in between. I have calculated the original volvo muffler to be about 6 litres.

Do I just need to calculate the volume of water in the exhaust hose downstream of the waterlock?

 

[Tranona]

It is the capacity of the exhaust system that determines the capacity (that is diameter and length of hose) and for the sort of boat a 2020 is fitted to 4.5l is the correct size and does hoses up to 50mm (2020 is 45mm). The capacity of the Volvo muffler is much the same at just under 5l. The Vetus watertrap is slightly shorter than the Volvo so you need to check that you can move the aft section of the pipe forward to mate up with the spigot. Consider having the Volvo end plate repaired. If it is the usual pinholes around the weld of the exit pipe then is should be possible to have a patch welded over. The one I had repaired cost £50.

 

[[70521]]

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[VicS]

The original Volvo Penta waterlock muffler on my MD2020 has developed a pinhole leak.

I am looking at buying a Vetus plastic replacement - much cheaper and more durable too. But how do I calculate the size required?

The Vetus mufflers seem to be available in either 4.7litres or 10.5 litres but nothing in between. I have calculated the original volvo muffler to be about 6 litres.

Do I just need to calculate the volume of water in the exhaust hose downstream of the waterlock?

See the on line Vetus catalogue for details of all waterlocks, mufflers and calculation of the required size
Page 101 et seq. here
VETUS catalogue 2021 - 2022 EN

The required capacity is based on 25% of the volume of the hose but includes a 2 times safety factor
( That makes it 1/2 the volume of the hose)

 

[Jokani]

These are my calculations for a 2020:

D = 45mm
L = 3000mm
Volume = (Pie/4) x D2 x L)
Pie = 3.14

=(3.14/4 = 0.785) x (45mm x 45mm =2025 ) x 3000mm = 7,768,875 x 0.25 / 1000000 = 1.192 litres x 2 for safety

Exhaust hose = 45mm ID exhaust capacity is 0.6 litres per metre

3m x 45mm ID = Appox 1.9 litres
4m x 45mm ID = Appox 2.6 litres

If my calculations are correct? The smaller muffler would be fine, and is the one a marine engineer fitted for me.