Sherwood MAXIMUS SRB5600 - worth keeping / paying to have serviced?

[ThatDogDontHunt]

and now getting back on topic...
I claim the OP has the choice of several roads:
1) Blindly trust your LDS and do what ever they say.
2) learn a little (or a lot?) and then be able to make your own judgements.

Blindly trusting a LDS is often the most expensive path (they are in business to make money after all). If you have no interest or ability to learn about your gear then this is the only road for you. This is often the best path for vacation divers. A downside to this path is that every now and then (but not very frequently or every shop would be out of business by now) a LDS service tech screws up a perfectly functioning reg. This is mostly discovered by the vacation diver when they gear up for their first dive of their trip at a remote location. Solution is to always do a gear checkout dive at home (in the LDS pool?) any time you get any gear serviced.

You appear to be taking the first steps to start down the other road. SB is a great place to learn. It contains lots of knowledge and lots of opinions.

My knowledge: There are lots of divers using equipment older than yours. My regs are around 10 years older than yours and working fine. Age is not an issue if the reg is treated properly and maintained.

My opinion: Since the reg has been sitting for a while it makes sense for it to be disassembled and checked out. It may work perfectly fine as-is? BUT: It may have some orings that have hardened, dried, taken a set or crumbled? It may have some crud inside? The only way to know is to have it examined internally. You also need to have the hoses examined. They may be perfectly fine. Or not?

 

[jakehbk]

Ooh... @rsingler is probably the guy to explain it better than I can with some fancy math and charts for the visual learners.

If I'm not mistaken the dry bleed system is the way the 1st stage compensates for increased ambient pressure at depth. It's a sort of built in IP creep via that flexible black vent plug. The more ambient pressure on the vent plug, the higher the IP climbs. No bubbles=no depth compensation.

Whether that results in a "noticeable" decrease at depth? Well you seem to not have noticed so there might be our answer.

 

[BRT]

I vaguely remember reading about this performance reduction at depth, but have not experienced it while diving with a non-functional dry bleed system.**

Can you provide an explanation of why a failed dry bleed is expected to lead to a change in performance? And would any change be expected to be noticed?

** Yes I dove a plugged reg for a while after my LDS did a christolube pack of the cap. The only side effect was moisture and crud in the cap which required a little extra cleaning to remove. AND a piston replacement (this was an older model) to get the dry bleed to work again.

Without the "leak" into the balance chamber the chamber doesn't adjust above surface pressure. The air "leak" pressurizes the chamber until it reaches ambient water pressure, thereby raising the intermediate pressure to compensate for depth. Any air above ambient just leaks out past he rubber mushroom valve.

 

[rsingler]

Sherwood was making quality regulators before Scubapro and Atomic even existed. They get no love out on the West Coast, but have some very imaginative designs. The dry bleed system is a perfect example that few divers understand.
As noted above, it doesn't require packing with lube like Atomic. It delivers great flow for recreational diving. As a balanced downstream first stage (that in itself is unusual) its LP ports are right next to the valve, as opposed to having to flow down the piston shaft, which makes up for the smaller valve orifice.
Also as noted above, the quick way to check on it is to pressurize the reg and submerge the first stage. It should bubble  slightly from the little black rubber stopper. About 13-27cc (half to one shot glass) every minute. If it doesn't, then buy a new reg unless you have a Sherwood shop you can trust. If it does bubble, and the IP is within specification, you're good to go! Very low maintenance, as long as you don't let a shop tech get lube in the little internal filter that controls the air bleed. In short, you really need a Sherwood shop. Or I have replacement air bleeds for that reg here in the shop.
And Northeast Scuba Supply sells service kits for $39.

 

[ThatDogDontHunt]

Without the "leak" into the balance chamber the chamber doesn't adjust above surface pressure. The air "leak" pressurizes the chamber until it reaches ambient water pressure, thereby raising the intermediate pressure to compensate for depth. Any air above ambient just leaks out past he rubber mushroom valve.

We know that if the dry bleed stops working then water gets into the ambient chamber via the one way valve. So the "one way valve" is not a one way valve. It will let pressure into the ambient chamber.

Lots of people have dunked unpressurized regs in rinse tanks without causing issues. So the one way valve will keep water out at rinse tank depths for at least short periods of time.

What is unknown is what the the time lag and pressure differential between ambient and the ambient chamber when at depth. i.e. how leaky is the one way valve?

 

[rsingler]

Actually, it is known. Based on a 27cc bleed rate, you'd have to descend to 300feet in 30 sec to overcome the bleed mechanism. If it were working at 20% capacity (not uncommon for poorly service regs) You'd have to descend to 66 feet in less than 60 seconds for the absolute IP to lag enough that your second stage reg would be challenged. That's why folks get away with close to non-functional Sherwoods.

 

[keyshunter]

Sherwood's dry bleed is important, but I have seen divers at recreational depths who had no idea that the dry bleed was not functioning. As long as the filter ( scintered filter in piston of older Sherwoods, or as a separate unit at the side in the first stage on later models) is not plugged, the dry bleed usually works flawlessly.

 

[BRT]

We know that if the dry bleed stops working then water gets into the ambient chamber via the one way valve. So the "one way valve" is not a one way valve. It will let pressure into the ambient chamber.

Lots of people have dunked unpressurized regs in rinse tanks without causing issues. So the one way valve will keep water out at rinse tank depths for at least short periods of time.

What is unknown is what the the time lag and pressure differential between ambient and the ambient chamber when at depth. i.e. how leaky is the one way valve?

There has to be a delay, but after many years using Sherwoods, there is a difference between when the dry bleed is working and when it is not working.

 

[Bob DBF]

Sherwood was making quality regulators before Scubapro and Atomic even existed.

Sherwood has been a precision manufacturer of high pressure valves, regulators, and equipment since the '30's. During the mid '50's they manufactured parts for viturually every SCUBA manufacturer of the day, that continued for quite some time until there were other manufacturers capable of the necessary precision. In the '70's they started manufacturing their own line of regulators.

In 1958, engineers from Sherwood Manufacturing modified the piston regulator for underwater. Several other manufacturers adopted the piston design over the other widely used diaphragm design. Sherwood held the patent, but never restricted its use by others in any way.