Technician brought his Landscape Sprayer in yesterday and said we wasn't getting any pressure. One look at his Diaphragm Pump and we could see it was leaking oil from the oil reservoir. He had tried to stop the leak by putting a plastic bag under the cap.
The cap to the oil reservoir was cracked. Once we replaced the cap, his rig worked fine. We asked him how long it had been leaking oil and he told us a couple of days. It seems that so much oil was leaking out, the pump couldn't maintain pressure.
He was lucky, if he had waited much longer and run the pump without enough oil, he would have trashed the pump, taking his weed control sprayer out of commission.
Morale of the story: If your spray pump has a problem or needs service, don't wait. Get it fixed. It is much cheaper to fix small problems than to wait for them to become big, i.e., expensive, problems.