Davit Operation 4

[altangs]

Dear All,
Are there any operations people here who can advise on how they would normally operate a vertical manway davit. I am particularly interested in the situation where the blind has to be lifted up say a couple of inches to clear obstacles before it can be swung away from the opening.
Typically a davit will have an eyebolt or similar. Do you just continue screwing the nuts until it raises the blind, or is this just a bad design? What are the alternatives?

I am currently looking at a design, whereby the head is 42” approximately 1000kg, but it must be raised about 100mm to clear the clamps before it can be swung away to access the vessel. Unfortunately we also don’t have the head room to fix a block and tackle.
Any advice would be much appreciated

 

[chaulklate]

First off, let me clarify that I am not an operations person but have been involved in davit design. Ordinarily, you will include enough thread engagement and clearance to lift the blind/head however much you require as you have indicated. You could also look into using a quick-opening-closure, or a swing-bolt closure.

 

[vesselfab]

generally speaking....a davit eyebolt (w/ unc threads) is not designe to lift the blind. Threads are for slight adjustments to align the bolt holes.

if you are looking to raise a 2300# blind 4", I would look at an oversized eyebolt with acme thread and handles welded on the nut.

the operations department will send you flowers the first time it is operated.

 

[doct9960]

altangs,

Another option is the hydraulic jack head lift, where you lift the davit with a jack and then swing the davit. Refer to the picture of the gray vessel with a red jack...

http://www.precisionfiltration.com/products/PDF/Headlifts and Closures.pdf

 

[austsa]

altangs,
Lifting a 1000kg blind via a davit is not easy, but doable. Eyebolt shank needs to be at least 1" dia.

 

[MJCronin]

I agree with doct9960..... the jack lift, operated in combination with a long eye bolt configuration seems best to me.

IMHO, the jack, however, could be hydraulic or manual.

You do need something to take the load off of those UNC threads as the hardware is adjusted.

 

[SnTMan]

Second (or is it third?) the jack idea. Simple to make and maintain. "Works good, lasts a long time."

Regards,

Mike

 

[rhg]

See PIP Standard VEFV1119 Column Davit up to 2000 lbs load

Regards

rhg

 

[altangs]

Thanks everyone.
Both the ACME thread lead screw and the hydraulic jacks are good ideas to resolve my problem, but I am still interested in how some of the operation guys use the normally designed davits with only an eyebolt and nut. We have supplied many vessels with 900lb 24” manways in the vertical position, and I often think it must be difficult to raise them especially when you have a RTJ joint.

 

[jtseng123]

altangs,
Attached is what I have designed for many heavy blinds, already in service for different projects, and haven't heard complaint ( Well, may be later). If you check stress carefully, it may be good for more than 3000 Lbs blind. Don't forget to grease the threads. It cost nothing.
Feel free to copy or modify.

 

[altangs]

Thanks jtseng123,
I too have done many davit designs, and I agree eye-rod and nut does work in principle. Like yourselfe, I have never had any complaints, but that doesn't mean there hasn't been any, just that I have never heard back from the operators.
Thanks anyway.

 

[jtseng123]

To raise the heavy blind, nut is not using. It may not work. I use a 3" OD rod, 3" long, bore and tap to match the eyerod threads, and full penetration weld the turning bar to it.

 

[Compositepro]

You could also use a chain fall hoist. These are compact, inexpensive, robust,and very easy to operate without tools.

 

[rhg]

Truck crane may be useful in this case, depends of inspection frecuency.

Regrads

rhg