I am a concrete pump operator of both open loop and closed loop systems.The open cicuit pumps use Rexroth AV11 pumps,the closed cicuit use Rexroth A4V pumps.Both systems have max.pressure settings of 350 bar.What are the advantages and disadvantages of these two systems,and with the closed system is there any ideas of maintaining the system in order to keep from breakdown due to charge pump failure?

Not enough info for a non Rexroth person to give an eductaed answer without a lot of time spent studying the mentioned pumps and knowing a lot more about the application of them.

Geneally speaking, Closed loop (Often called Hydro(a)-Static circuts) are a lot more Energy Efficient since flow can be varied without throttling so energy input matches energy output so closely that little wasted energy (Heat Generation) is involved.
The only charge Pump problems I've seen are from over pressure operating conditions and/or High Contamination.

Opem loop system problems are often due to Heat Generation since Throttling is require when variable speed is necessary which means more energy is going in than being used and the excess energy winds up as HEAt.

I can imagine the operating conditions are not all that clean and if the circuts do not have very good filtration practices and all possible ingest of contamination openings are completely closed or protected so contamination is not able to get into the oil.

Your request need to be addressed by a reliable Fluid Power consultant who can go over the present design and make recommendations for permanent fixes. Anything more tha general help is almost impossible from a forum like tis unless you happen to luck on to a person with a similar application and proble they have already solved.

A GUESS IS CONTAMINATION BUT THE FIX IS MULTI'FACETED AND NOT CHEAP. OF COURSE SCRAPPING $12,000.00 pumps on a regular basis is'nt cheap either.

Maybe others can shed more light on the subject and be of more help.

Thank you for responding to my questions.The one time I lost a charge pump,internal gear came apart,was when the machine was cycled with cold or lower than optimal operating temperature.I am in southern Louisiana so cold means 45 F.I will keep in my mind your suggestion about oil contamination causing breakdown.I am a fan of the closed circuit pumps that we use as they cycle so smoothly and have good pressure output,as compared to our open circuit machines that tend to bang when cycling.The open circuit machines are made by Schwing America in White Bear Minn.,the closed circuit machines are made by Putzmeister in Racine Wis.,both use Rexroth hydraulic pumps.

I would be using an Off-Line Filter setup that takes oil from one end of the tank , through a 3 Micron filter and back to the tank. You can determine the amount of contamination qickly by how fast the filters go into bypass.

Some distributors rent portable units if you don't want to buy one. I always specify an Off-Line filter setup on all new installations. What they save in components is just a drop in the bucket for what they save on Downtime.

That is if the oil looks at all dirty. Any oil that shows contamination is way past the cleanliness level recommended by most pump manufacturers. The smallest particles a person with good eyesight can see is around 40 Micron and no pump manufacturer recommends anywhere near that level of contamination for their pumps.

Another thing I've seen that increased pump life on cool/cold start-up and warm/hot running is to use 10W40 or 20W50 Egine oil in the hydraulic circuit. That oil holds up so well in a lot more heat, component load and contamination than a normal hydraulic circuit sees it seemed like a No-Brainer when I first heard about it from a customer who had always used it in his Fertilizer trucks.

His original reason for changing the hydraulics to engine oil was, a mechanic had mistakemly used hydraulic oil in an engine and it did'nt last very long. So he decided that would not happen again since there would only be one kind of oil in the shop, the 20W50 he used year round in his trucks engines.

He reasoned if it held up in engines that saw a lot more torture it should hold up in the hydraulic circuits.

I've suggested using engine oil to a lot of Mobile equipment customers and a few Industrial ones with great success.

my friend i think the closed systen is used specialy to machine have to direction the closed system can change the direction

Just wondering if your transmission pump(A4VG) is direct engine mounted or PTO drivin? I have seen premature charge pump failure due to an offset PTO drive, apparently it causes excessive axial load to the rear of the pump shaft were the charge pump is drivin, the single parallel key that drives the internal gear flogs out causeing the charge pump to fail.