Technical Query. Diesel exhaust pressures.

[oldgit]

Have finally got up the cojones to fit some waterlock silencers to my boat,they have been lurking in the garage for ages.Some might like the roar of a straight through exhaust but it does get wearing on long journies.
Bit apprehensive that a lot of work and expense would not amount to much noise reduction,however,noise reduced much better than expected.
However now need to check that back pressure is within the limits set in the Perkins installation manual.Inches of Mercury apparently ?
There is a small tapping on the exhaust riser which assume is for inserting probe on pressure measuring device.
Question is, what do I need to do the job, we are surrounded by various garages and engineering workshops,which door do I knock on the to borrow one.

 

[essexboy]

Unless you know what the back pressure is now , you will not know if has been affected by the installation of water locks.
" man without data can ony express opinions "

 

[Latestarter1]

Maximum of 3 inches of Hg at W.O.T

You need to confirm tapping size on exhaust elbow, many use 1/8th NPT.

PM me can sort you out with something.

 

[oldgit]

Thanks for replies.
The grub screw blanking off the hole does appear to be very small.Will consult manual for details or remove grub screw for thread and dimensions.
Did throttle up to WOT no load to check water volume out of exhaust ,curious that RPM maxed out at 2800 ish where as max RPM is supposed to be 2600. Engines are basic 130 hp naturally aspirated.
Going to assume we actually need to be underway in order to check any loss of RPM at WOT.

 

[Latestarter1]

Thanks for replies.
The grub screw blanking off the hole does appear to be very small.Will consult manual for details or remove grub screw for thread and dimensions.
Did throttle up to WOT no load to check water volume out of exhaust ,curious that RPM maxed out at 2800 ish where as max RPM is supposed to be 2600. Engines are basic 130 hp naturally aspirated.
Going to assume we actually need to be underway in order to check any loss of RPM at WOT.

Yes confirm that you will need to test at WOT loaded.

Your high idle sounds spot on. If engine rated speed is 2,600 rpm governor does not cut fueling off at this point it simply starts to reduce fueling progressively after rated speed is reached. Mechanical marine engine 'droop' is generally 10% therefore your 2,800 ish is spot on.

 

[oldgit]

Found this on the interweb. Scania Australia.
Simple device for checking backpressure on page 13...presumably if you are in the outback,not sure if there are very many marine engines in the interior. ?


]im_iin_m0204en-GB04.xml

 

[Latestarter1]

Found this on the interweb. Scania Australia.
Simple device for checking backpressure on page 13...presumably if you are in the outback,not sure if there are very many marine engines in the interior. ?


]im_iin_m0204en-GB04.xml

Water manometer is no problem in theory, however in practice getting a reading using a manometer in anything in other than a perfect sea is a nightmare.

100 millibar is 2.95 inches OK however 1 meter downstream of turbo is nuts, Scania application engineer who wrote topic this must have been smoking!

Real smart to bore a hole in rubber exhaust exhaust.

Your Perkins riser has tapping in the correct place.

 

[oldgit]

Mufflers installed and running... Real World Results.

Quick run out this morning,get temps up and then WOT to check for max revs and no leaks.
No change in max revs or engine T & Ps.
Dramatic reduction in external exhaust noise,you can actually now hear the wash behind the boat,unexpected considerable noise reduction inside boat as well.
Definately worthwhile in benefits in money and time.
Just got to check BP before season starts.

 

[Robg71]

Re: Mufflers installed and running... Real World Results.

I have been tempted to do this with my sabres...
noisy old brutes have straight through five inch pipework.
My mate heard my coming from about 5 mile away on a calm day...

 

[John100156]

Re: Mufflers installed and running... Real World Results.

OK just in case you have a different pressure gauge laying around, here's a few conversions for pressure at 3" mercury (100mbar is 2.95 in mercury, as L8 said):

3.3984 ft of water
40.782 in of water
1.4733 psi
76.191 Torr
101.58 mbar
0.10158 Bar
10.158 kPa
0.10025 Atmospheres
103.58 cm water
5.3635 g/cm2
23.573 Oz/dq in
0.0010358 kg/mm2
0.094712 Ton/sq ft
0.10358 kg/cm2

The list goes on, and on, and on.....

 

[oldgit]

Re: Mufflers installed and running... Real World Results.

I have been tempted to do this with my sabres...
noisy old brutes have straight through five inch pipework.
My mate heard my coming from about 5 mile away on a calm day...

My engines are the M135 6 litre Sabres.The exhaust exited via about 4m of 75mm hose directly out of the transom just above waterline.You would have thought the noise would have been directed astern and away from the boat,especially when moving.
However most of it managed,presumably by reflection off the water, to assault the eardrums back on board.
Soundlock do list a larger version of my mufflers but suspect for those with more powerful engines the cost of purchase and installation is going to be prohibitive.
Still at bit of a loss as to why most boats do not have any sort of noise control installed from new.

 

[oldgit]

Re: Mufflers installed and running... Real World Results.

OK just in case you have a different pressure gauge laying around, here's a few conversions for pressure at 3" mercury (100mbar is 2.95 in mercury, as L8 said):

3.3984 ft of water
40.782 in of water
1.4733 psi
76.191 Torr
101.58 mbar
0.10158 Bar
10.158 kPa
0.10025 Atmospheres
103.58 cm water
5.3635 g/cm2
23.573 Oz/dq in
0.0010358 kg/mm2
0.094712 Ton/sq ft
0.10358 kg/cm2

The list goes on, and on, and on.....

Cheers have printed this. OG.

 

[omega2]

Re: Mufflers installed and running... Real World Results.

https://youtu.be/KqfZ6ZXl5pc

Of course they make noise, but it's "Beautiful" Neil Diamond. !!

Sabre 180's